Responsibilities
Responsibilities should be single and clear. If describing a class needs the word “and”, it is probably two classes.
Python for Kids · Class 10 · Module 3 of 9
Object-Oriented Design
Good design is mostly deciding what each part is not responsible for.
8 sessionsSessions 17–24
4 weeksTypical pace
Intermediate to AppliedLevel
Class 10Python & Coding
The big idea
Students design object systems for real domains, assigning responsibilities deliberately, preferring composition to deep hierarchies, and judging their design by how easily it absorbs a new requirement.
Why it matters
Design quality determines whether a codebase can grow. It is the difference between adding a feature in an hour and rewriting for a week.
Unpacked
What you will actually learn
Three core ideas, each taught with worked examples and then practised until it feels obvious.
Composition
Composition builds capability by assembly, keeping parts swappable and independently testable.
Design clarity
Design clarity is measured practically: can a new person understand it, and can a new requirement be added without breaking three other things?
Did you know?
The Single Responsibility Principle is the S in SOLID, a set of five design principles that remain the industry’s common vocabulary.
Common mix-up
“More classes means better design.” Over-engineering is a real and common failure. The right number of classes is the fewest that keeps things clear.
Session by session
Your 8-session journey
Sessions 17–24 of the 72-session year, at two one-hour sessions per week.
- 1
Warm-up and big picture
Where this module fits, what you will build, and a hands-on starter that gets everyone curious about responsibilities.
- 2
Responsibilities
Guided teaching on responsibilities, worked through together with the teacher.
- 3
Responsibilities — practice lab
Independent practice, small challenges and one deliberate mistake to diagnose.
- 4
Composition
Guided teaching on composition, building directly on the previous two sessions.
- 5
Composition — practice lab
Applied tasks that combine responsibilities and composition in one piece of work.
- 6
Design clarity
Design clarity introduced and practised, completing the toolkit needed for the project.
- 7
Project build
Guided build session for the module project: Real-world domain model.
- 8
Test, present and reflect
Finish, test against the checklist, present the work and explain the decisions behind it.
Project lab
Real-world domain model
Every module ends with something the student built themselves and can demonstrate. This is the piece that goes into their portfolio and gets explained out loud at the end of session 24.
Try this at home
Model a real domain, then add an unplanned requirement. Count how many files you had to open — that number is your design score.
It is finished when
- It works from start to finish without breaking
- You can explain every part of it in your own words
- You tested it and improved at least one thing afterwards
- Someone else used or understood it without your help
By the end of this module
Students finishing Module 3 can:
- Explain and use responsibilities without prompting
- Explain and use composition without prompting
- Explain and use design clarity without prompting
- Build and finish real-world domain model
- Test your own work and correct what you find
- Talk an adult through what you made and why
Word bank
The vocabulary introduced here, in plain language:
- domain model
- Code that represents real-world concepts.
- coupling
- How much one part depends on another.
- cohesion
- How well the parts of a unit belong together.
Module challenge
Think you have got this?
0 XPLevel 1 · Curious Beginner
6 quick questions drawn from this module — vocabulary, the project you build, and a myth-or-fact round. Every wrong answer explains itself, so a mistake still teaches you something.
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