For teachers

Python in class – without accounts.

No registration, no student data on a server, no third-party services. Students open the page and get going – Python runs entirely in the browser.

🔒 Data-minimal

Progress stays in the student's browser. There are no cookies, tracking or accounts. Details are in the privacy policy (German).

✓ Instant feedback

Every task is checked automatically, error messages are explained clearly, and staged hints help before the solution appears.

🤖 Robotics without hardware

The Pybricks simulator lets everyone program at the same time – even with only a few LEGO SPIKE sets. The code then runs unchanged on the real robot.

📶 Offline in the classroom

Poor Wi-Fi? Press the button once on each device while online – after that all lessons, the training room and Python work without a connection. What you saved stays after updates and is refreshed automatically next time you are online. Codelix can also be installed like an app from the browser menu.

📄 Worksheets and model solutions

Every lesson has a “Print worksheet” button at the top: text, examples and task with writing lines, name/date and a QR code back to the lesson. Without hints or the solution – the pro task gets a page of its own.

All model solutions (including the pro tasks) are collected for teachers – unlocked with a question from the book “Python für Roboter”.

🔑 To the model solutions

What a lesson can look like

Warm-up (5 min) – Everyone does the tasks of the day – the same for everyone, good for comparing.
New topic (15 min) – Read the lesson together, run the examples, show memory with “Steps”.
Task (15 min) – Alone or in pairs; the check gives instant feedback.
Practice (10 min) – Training room on the topic; fast learners try puzzle and fix-the-bug tasks.
Hand-in – Send a link to the code with “Share”, or save the progress file at the end of the lesson (see below).

Tip to start: placement test – so everyone sees where to start. Everything important is also on the cheat sheet.

Lesson plans to print

For every area a plan for 45 and for 90 minutes – with the sequence, differentiation and the mistakes that come up in almost every class.

Python

45 minutes: Write first programs with variables, print() and if.

Lessons: Hello, Python!, Decisions with if

Min	Sequence
5	Warm-up: what is a program? Run an example together and change a number.
15	Read the lesson “Hello, Python!” together, run the examples, show variables with “Steps”.
15	Task alone or in pairs. Use the hint ladder instead of asking straight away.
7	Quick check “What does this print?” together: guess first, then check.
3	Wrap-up: one pupil explains their program. Preview of if.

For fast learners: Pro task “digital clock” and the lesson “Decisions with if”.

More support: Only the first line of the task; deliberately allow the gap code (hint 3).

Typical mistakes in class:

Text without quotes: print(Hello) → NameError.
Joining a number and text with + → TypeError (show f-strings).
Upper/lower case: Print instead of print.

90 minutes: Analyse data with loops and lists.

Lessons: Loops – repeating things, Lists – many values at once

Min	Sequence
10	Warm-up: today's tasks in the training room – the same for everyone.
20	Loops: for with range() together, “Steps” shows every pass.
15	Loop task, then a short discussion of typical errors.
5	Break / movement
20	Lists: create, index, append – run and change examples.
15	List task (max, average, counting).
5	Wrap-up: who earned a ⭐ without help? Preview of functions.

For fast learners: Pro tasks “number pyramid” and “second largest number”, then training room “Fix”.

More support: Training room “Predict” for loops only; use the gap code.

Typical mistakes in class:

Forgetting the colon after for or wrong indentation → SyntaxError/IndentationError.
range(1, 10) stops at 9 – “one too few”.
Index from 0: list[1] is the second element.

Robotics with LEGO SPIKE

45 minutes: Make a robot drive precisely in the simulator.

Lessons: Your first Pybricks program, Driving with the DriveBase

Min	Sequence
5	Warm-up: show a real SPIKE (if available) or the simulator – ports, motors, hub.
15	First program and DriveBase together: try straight() and turn().
20	Task “drive a triangle” in the simulator; speed 4× for quick testing.
5	Wrap-up: why does the real robot never drive exactly? (calibration as a preview)

For fast learners: Robotics challenge “Sprint” or “Slalom” – share the best time as a link.

More support: Only straight ahead and one turn; follow the starter code line by line.

Typical mistakes in class:

turn(90) turns clockwise – sign mixed up.
mm and cm mixed up: straight(20) is only 2 cm.
Turning 60° instead of 120° for the triangle (exterior angle).

90 minutes: React to the surroundings with sensors and understand a P controller.

Lessons: Sensors – colour, distance, force, Following lines with a P controller

Min	Sequence
10	Review DriveBase: a short driving task without help.
20	Sensors: colour, distance, force – look at readings with print() and in the live chart.
15	Sensor task.
5	Break
25	Line follower: on/off control vs. P controller, change KP and observe.
10	Mini competition: who drives the lap most smoothly? Then: competition “Warehouse” as a preview.
5	Wrap-up: what does KP do?

For fast learners: Competition “Warehouse” (100 points in 60 s) or an own course with missions.

More support: Colour sensor only: stop at red. Give KP and just observe.

Typical mistakes in class:

Endless loop without wait() – the robot “hangs”: show the Stop button.
KP far too large → the robot wobbles.
The sensor port in the code doesn't match the build.

Robotics with fischertechnik

45 minutes: Control motors and lamps on the TXT 4.0 with ftrobopy.

Lessons: The TXT 4.0 and ftrobopy, Controlling XS motors

Min	Sequence
5	Warm-up: show the M, O, I, C ports on a real TXT or in the control panel.
15	Connecting and lamps: print() and a lamp as feedback.
20	Motors: setSpeed(), then setDistance() with finished() – task “barrier”.
5	Wrap-up: why does setDistance() need setSpeed() first?

For fast learners: Do the “light organ” exercise from lesson 3 early.

More support: Only change xs_motor.py: adjust speed and duration.

Typical mistakes in class:

setDistance() without setSpeed() → motor stands still, finished() waits forever.
Ports counted from 0 – in ftrobopy M1 = motor(1).
Forgetting sleep() – the lamp only flashes briefly.

90 minutes: Read sensors and buttons and program a traffic light as a sequence of states.

Lessons: Lamps and buttons, Line tracker and phototransistor, Project: Traffic light control

Min	Sequence
10	Review: lamps on/off, light organ.
15	Buttons: try the reversed logic (0 = pressed) together.
20	Sensors: phototransistor with the slider, sensor logger as the task.
5	Break
30	Traffic light project: read the code, states on the board, then program night mode.
10	Demo and short reflection: where are states in everyday life?

For fast learners: Extend the pedestrian request or an own project from the book (sorting machine).

More support: Traffic light with only three states and no button.

Typical mistakes in class:

Button logic reversed: assuming state() == 1 means “pressed”.
Threshold guessed instead of measured.
Forgetting all_off() → two lamps on at the same time.

JavaScript

45 minutes: Design an own web page with HTML and CSS.

Lessons: Your own web page: HTML and CSS

Min	Sequence
5	Warm-up: right-click → view source of a well-known page – “that's HTML”.
15	Tags and CSS together: the live preview shows every change at once.
20	Task: own profile page with a list and a class.
5	Gallery walk: show two pages on the projector.

For fast learners: Continue with “DOM and clicks”: a button that changes the colour.

More support: Only change text and one colour; web pages have no gap code – copy an example and adapt it.

Typical mistakes in class:

Forgetting the closing tag: <h1>Title without </h1>.
Forgetting the semicolon in CSS – the next property doesn't work.
Writing the dot in HTML: class=".hobby".

90 minutes: React to clicks with JavaScript and build a small browser game.

Lessons: Web pages with JavaScript: DOM and clicks, Drawing with canvas, Project: click hunt in the browser

Min	Sequence
10	Review HTML/CSS: improve the profile page in 5 minutes.
20	DOM and clicks: querySelector, textContent, addEventListener – click counter.
15	Canvas: draw shapes, traffic light task.
5	Break
30	Project click hunt: write hit(), then own ideas (smaller target, restart).
10	Class tournament: who gets the most hits in 20 seconds?

For fast learners: Rebuild the click hunt with a canvas instead of a button.

More support: Only the click counter; use the console below the preview for console.log.

Typical mistakes in class:

querySelector("number") instead of "#number" → null.
Script at the top of the HTML – the elements don't exist yet.
Forgetting "px" with style.left.

Programming games

45 minutes: Understand a game loop and steer a figure with keys.

Lessons: Your first game: shapes, loop, keys

Min	Sequence
5	Warm-up: flip book – why does movement look smooth?
15	Drawing shapes and coordinates (y points down!) on the board.
20	Task: steer the player and keep it inside the window.
5	Wrap-up: what happens 30 times a second?

For fast learners: Start the catch game lesson or add own shapes/colours.

More support: Only right and left; the edge as a second step.

Typical mistakes in class:

y grows downwards – “up” means making y smaller.
Normal variable instead of a dictionary in the function → UnboundLocalError.
game.run(update()) with brackets.

90 minutes: Build a complete game with collision, points and game over.

Lessons: Project: catch game, Project: snake game

Min	Sequence
10	Review game loop: a ball from left to right.
20	Rectangle collision on the board with two paper rectangles.
20	Catch game: hits() and points.
5	Break
25	Snake game: list as a snake, move() and is_over().
10	Play round: try each other's games and give feedback.

For fast learners: Paddle duel with a computer opponent; then two players with W/S.

More support: Catch game without lives; hits() with the gap code.

Typical mistakes in class:

<= instead of < in the collision – touching counts as a hit.
pop() also when eating – the snake doesn't grow.
Reversing direction directly – the snake bites itself.

Exploring computer science

45 minutes: Understand how computers store numbers and text as bits.

Lessons: Binary numbers, bits and bytes

Min	Sequence
10	Warm-up: lights on/off with 4 lamps (pupils) – which number is it?
15	Place values 8-4-2-1, try converting with int() and bin().
15	Task to_binary() with % and //.
5	Wrap-up: quick check and “how many values fit in a byte?”

For fast learners: Continue with encryption (Caesar).

More support: Only convert numbers up to 15 on the board; task with the gap code.

Typical mistakes in class:

Remainders joined in the wrong order.
Forgetting the special case 0 → empty text.
/ instead of // → decimal numbers.

90 minutes: Understand encryption and search engines as algorithms.

Lessons: Secret codes – Caesar and Vigenère, How does a search engine work?, How fast is an algorithm?

Min	Sequence
10	Warm-up: crack a secret message on the board (Caesar) together.
20	Caesar and brute force in Python, then explain Vigenère.
15	Vigenère task; pairs send each other encrypted messages.
5	Break
20	Search engine: show a book's index, index as a dictionary with sets.
15	How fast? Count handshakes in the class (n · (n − 1) / 2) and compare with Python.
5	Wrap-up: why is Vigenère still insecure today?

For fast learners: Pictures as pixels: own filters (mirror, blur).

More support: Only Caesar; search engine without cleaning punctuation.

Typical mistakes in class:

Forgetting % 26 → characters after Z.
Key letter also advanced on spaces.
Joining sets with + instead of & or |.

Lessons at a glance

Python

#	Lesson	Time	Goals
1	Hello, Python!	15 minutes	Print text and numbers with print() · Create and use variables · Combine text and numbers with f-strings
2	Decisions with if	20 minutes	Read input with input() and turn it into numbers with int() · Compare values (<, >, ==, …) · Take different paths with if, elif and else
3	Loops – repeating things	20 minutes	Run code several times with for and range() · Repeat with while as long as something is true · Recognise and avoid endless loops
4	Project: Drawing with the turtle	45 minutes	Draw lines, shapes and colours with the turtle · Use loops and functions to create patterns · Program your own artwork and save it as a picture
5	Lists – many values at once	25 minutes	Create lists and access items by position (index) · Append, change and count items · Analyse lists with sum(), max() and a loop
6	Working with strings	25 minutes	Cut out single letters and pieces of text · Change text with upper(), lower() and replace() · Count letters with a loop
7	Project: Hangman	40 minutes	Process text letter by letter · Work with a set of guessed letters · Build a complete guessing game with a while loop
8	Dictionaries	25 minutes	Store data as pairs of key and value · Look up, change and add values · Go through all pairs with items()
9	Project: text adventure	45 minutes	Build a game loop with while · Store a game world as a nested dictionary · Check input and react clearly
10	Your own functions	30 minutes	Write your own functions with def · Pass values in with parameters and give them back with return · Reuse functions inside other functions
11	Bug detective: finding bugs	30 minutes	Read error messages from the bottom up · Find bugs that don't produce an error message · Look inside a program with print() and “Steps”
12	Project: quiz game	45 minutes	Organise data as a list of dictionaries · Compare answers tolerantly and count points · Split the program into functions
13	Boss level: the school report program	45 minutes	Combine everything from the beginner stage in one project · Analyse data with dictionaries, loops and functions · Present a result clearly
14	Catching errors with try	25 minutes	Understand when programs crash · Catch errors with try and except · Handle different kinds of errors differently
15	Tuples and sets	30 minutes	Use tuples as unchangeable pairs of values · Remove duplicate values with sets · Form intersections, unions and differences
16	Reading and writing files	25 minutes	Write and read files with open() and with · Process the lines of a file · Append data to a file
17	JSON – saving data like the pros	30 minutes	Understand what JSON is and where it's used · Save and load dictionaries and lists with json · Keep working with saved data
18	Project: guessing game with high score	45 minutes	Build a game with a while loop and break · Save a record in a file and load it again · Catch a missing file with try/except
19	Modules – ready-made toolboxes	25 minutes	Import modules like math and random · Tell import, from … import and as apart · Write and use your own module
20	Your own tests with assert	25 minutes	Check with assert whether code calculates correctly · Find and test edge cases · Write test functions like the pros
21	List comprehensions	25 minutes	Create lists in a single line · Filter with if inside a comprehension · Write dictionary comprehensions
22	Project: weather station	45 minutes	Store measurements in lists and go through them in pairs with zip() · Calculate the average, minimum and maximum · Show data as a bar chart made of text
23	Project: tic-tac-toe	45 minutes	Represent a board as a list of lists · Check rows, columns and diagonals · Split a game into clear functions
24	Classes and objects	35 minutes	Write your own blueprint for objects with class · Set attributes in __init__ and use them through self · Write methods that change an object
25	Inheritance – extending classes	30 minutes	Let one class inherit from another · Override methods and extend them with super() · Check what an object is with isinstance()
26	Special methods and @property	30 minutes	Decide with __str__ how print() shows an object · Compare and calculate with objects using __eq__, __lt__ and __add__ · Write calculated attributes with @property
27	Bug detective 2: classes and exceptions	35 minutes	Read longer error messages (tracebacks) step by step · Find bugs in classes (forgotten self, wrong calculation) · Check things deliberately with assert and f"{x=}"
28	Boss level: the library	60 minutes	Design your own class with several methods · Report errors with your own exceptions · Save data in a file and load it again
29	Recursion – functions that call themselves	40 minutes	Understand how a function can call itself · Tell the base case from the recursive step · Break problems down into smaller problems of the same kind
30	Algorithms – searching and sorting	45 minutes	Understand what an algorithm is · Compare linear and binary search · Program a sorting algorithm yourself
31	Generators and yield	25 minutes	Write functions with yield · Understand why generators save memory · Use generators with next(), for and sum()
32	Decorators	30 minutes	Pass functions around as values · Write your own decorator · Extend a function with @
33	Type hints	20 minutes	Label parameters and return values with types · Read list[int], dict[str, int] and optional values · Use dataclasses for simple data objects
34	async and await	30 minutes	Understand what “waiting at the same time” means · Work with async def, await and asyncio.run · Run several tasks in parallel with asyncio.gather
35	Boss level: the data pipeline	60 minutes	Use generators, decorators and type hints together · Skip faulty data robustly · Write professional, readable code

Robotics with LEGO SPIKE

#	Lesson	Time	Goals
1	Your first Pybricks program	20 minutes	Import Pybricks building blocks · Control the hub with scrolling text, light and icons · Add pauses with wait()
2	Driving with the DriveBase	30 minutes	Combine two motors into a DriveBase · Drive precisely with straight(), turn() and arc() · Watch movements on the side with wait=False
3	Sensors – colour, distance, force	30 minutes	Read the colour sensor, ultrasonic sensor and force sensor · Use the pattern “measure, check, react” · Combine driving and measuring
4	Following lines with a P controller	30 minutes	Understand why on/off steering jerks around · Build a P controller from error and gain · Tune KP and speed sensibly
5	Buttons and gyro sensor	25 minutes	Wait for a button press on the hub · Measure the heading with the gyro sensor · Calculate the shortest turn angle with modulo
6	Display and sounds	25 minutes	Build your own image as a list of lists · Control single pixels and their brightness · Calculate a status display from measurements · Play sounds and melodies
7	Calibrating	30 minutes	Understand why real robots never drive perfectly · Measure the distance with the distance sensor and the turn with the gyro · Recalculate wheel_diameter and axle_track correctly
8	Moving to the real SPIKE	30 minutes	Put Pybricks onto the SPIKE hub · Transfer programs from the simulator to the real robot · Measure sensor values before the first run instead of guessing

JavaScript

#	Lesson	Time	Goals
1	Hello, JavaScript!	25 minutes	Print something with console.log() · Create variables with let and const · Build text with template strings
2	Decisions with if	25 minutes	Branch with if, else if and else · Compare values with === · Combine conditions with && and \|\|
3	Loops	30 minutes	Count with for · Repeat with while as long as something holds · Add up results in a loop
4	Arrays – many values at once	30 minutes	Create arrays and read values by index · Add values with push and go through them with for…of · Process arrays with filter and map
5	Functions	30 minutes	Write functions with function · Return values with return · Use arrow functions (=>)
6	Objects	30 minutes	Create objects with properties · Read and change properties · Work with arrays of objects
7	Project: guess the number	35 minutes	Ask for input with prompt() · Turn text into numbers with Number() · Build a complete game with while, if and counters
8	Your own web page: HTML and CSS	35 minutes	Write a web page with a heading, paragraphs and lists in HTML · Set colours, spacing and font sizes with CSS · Style several elements the same way with classes
9	Web pages with JavaScript: DOM and clicks	40 minutes	Find an element on the page with document.querySelector · Change the text and look of an element with JavaScript · React to clicks with addEventListener
10	Drawing with canvas	35 minutes	Paint rectangles and circles on a drawing area (canvas) · Draw patterns with loops · Change a drawing with a click
11	Project: click hunt in the browser	45 minutes	Put an element at a random place with JavaScript · Make a clock count down with setInterval · Combine HTML, CSS and JavaScript into a finished game

Robotics with fischertechnik

#	Lesson	Time	Goals
1	The TXT 4.0 and ftrobopy	25 minutes	Know the M, O, I and C ports of the TXT 4.0 · Connect to the TXT with ftrobopy · Give feedback with print() and a lamp
2	Controlling XS motors	30 minutes	Run an XS motor forwards and backwards with setSpeed() · Drive an exact distance in encoder pulses with setDistance() · Wait with finished() until a movement is complete
3	Lamps and buttons	30 minutes	Switch lamps on O1 to O8 on and off and dim them · Read a button on an I input · Understand the reversed logic of state() (0 = pressed)
4	Line tracker and phototransistor	30 minutes	Detect with the line tracker whether a line is under the sensor · Measure brightness as a voltage in mV with the phototransistor · Collect readings in a list and analyse them
5	Project: Traffic light control	45 minutes	Program a traffic light as a sequence of states · Keep the code readable with small helper functions · React to a pedestrian request with a button

Programming games

#	Lesson	Time	Goals
1	Your first game: shapes, loop, keys	30 minutes	Draw shapes and text on a game area · Understand how a game loop works frame by frame · Steer a figure with the arrow keys and keep it inside the window
2	Project: catch game	45 minutes	Make things appear at random places with random · Check whether two rectangles touch (collision) · Count points, take away lives and end the game with game.stop()
3	Project: snake game	60 minutes	Build a game area made of squares with game.grid() and game.cell() · Store a snake as a list of positions and let it grow · Change direction with game.pressed() and detect the end of the game
4	Project: paddle duel	60 minutes	Move a ball with a speed in x and y direction · Let the ball bounce off walls and paddles · Program a simple computer opponent

Exploring computer science

#	Lesson	Time	Goals
1	Binary numbers, bits and bytes	35 minutes	Understand why computers only calculate with 0 and 1 · Convert numbers between the decimal and the binary system · Know how letters are stored as numbers
2	Secret codes – Caesar and Vigenère	45 minutes	Understand and program the Caesar cipher · See why Caesar is easy to crack · Encrypt more securely with a keyword using Vigenère
3	Pictures are made of pixels	40 minutes	Store a picture as a list of rows with brightness values · Understand how colours are made from red, green and blue · Program your own image filters
4	How does a search engine work?	45 minutes	Understand why search engines don't read every page one by one · Build an index of words and pages · Use sets to find pages that contain several words
5	How fast is an algorithm?	40 minutes	Count a program's steps instead of timing it · See how the number of steps grows when the data gets twice as big · Replace a slow algorithm with a fast one

🔗 Class link: choose lessons for your class

Tick the lessons above that your class should work on and give the list a name. The link only contains this selection – no student names, no account. Whoever opens it sees exactly these lessons with their own progress.

Name of the list

Class overview – without a server

1. Students go to “My progress” → “Save as file” and give you the file (e.g. via your school's learning platform), ideally with their name in the file name.
2. Select all files here at once. They are only read in your browser – nothing is uploaded or stored.

Choose progress files

🏁 Class leaderboard for the robotics challenges

Students send you their links from “Share time”. Paste them here – one per line, “Name: link”. Every time is re-checked in the simulator, so faked times stand out. Everything happens only in your browser.

Students' links