Lesson 16: Refactoring and Changing Existing Systems Safely (Teach This Topic)

This guide supports teaching learners aged 11 to 16 how to judge AI suggestions for changes to existing software. It explains refactoring, bug fixing, feature development and migrations, then links these ideas to interfaces, dependencies, legacy code, staged changes and regression risk. All discussion and written tasks are self-contained and require only paper and a pen or pencil; no code needs to be edited or run.