A 60-minute lesson on binary search. It starts with a “guess my number” game, then the slides show low, mid and high moving as half the list is thrown away at each step. Pupils find midpoints, list the items checked, and see why binary search needs a sorted list.

Lesson outline

• Do now: guess my number from 1 to 100
• The binary search rules, and finding the middle with (low + high) ÷ 2
• Step-through: find 46, with low, mid and high labelled
• Step-through: an item that isn’t in the list
• Linear vs binary: a worst-case table from 10 items to a million
• 15 minutes on the interactive drill
• Exit ticket: can you use binary search on this list?

Included: slides.html and slides.pdf · lesson-plan.pdf · drill.html (11 questions, including Python predict-the-output and spot-the-bug) · worksheet.pdf with answers · how-to-use.pdf

National Curriculum KS3: key algorithms for searching, and comparing alternative algorithms for the same problem. Works offline. No logins.