High School Python Debugging Lesson Plan

Learning Objectives

• Identify and classify syntax, runtime, and logic errors in Python code.
• Apply a systematic debugging strategy (read, run, trace, fix).
• Explain their debugging process clearly to a peer.

• Display 3 short Python snippets, each with a different error type (syntax, runtime, logic).
• Students identify the error type and predict the error message for each.
• Quick class review: 'What clues helped you identify each type?'

• Introduce the 4-step strategy: Read the error message, Run with print statements, Trace the logic, Fix and re-test.
• Live demo: debug a function with a logic error using the 4-step process.
• Post the strategy poster for reference.

• Pairs receive 4 buggy Python programs of increasing difficulty.
• For each: identify the error type, apply the 4-step strategy, fix the code, document what they changed and why.
• Teacher circulates and asks: 'What step are you on? What did the error message tell you?'

• 3–4 pairs present their hardest bug fix to the class.
• Explain: what was the bug, what strategy helped, what they changed.
• Class asks clarifying questions.

• Exit ticket: 'Given this error message, what would be your first two debugging steps?'
• Collect. Preview: 'Tomorrow we tackle debugging in a larger project.'

Assessment

• Student product: 4 fixed programs with documentation of changes.
• Criteria: Correct fix for each bug, accurate error classification, clear documentation.
• Success indicator: 80% of pairs correctly fix at least 3 of 4 bugs.