Understand
A single percentage can hide uneven performance. If a test contains nine blue cards and one green card, a system that always says blue scores 9/10 while failing every green example. Record the test composition and errors by relevant category. A small constructed example demonstrates a limitation; it is not evidence about a real product.
Original classroom scenario / sample claim
A paper classifier scores 90% on nine blue cards and one green card by predicting blue for every card. Its report says both colours are recognised well.
Try it and check it
- Draw the ten cards and write the prediction beside each.
- Calculate overall correct/total and correct/total for each colour.
- Explain which conclusion the overall percentage hides.
- Propose an additional test that would reveal the weakness clearly.
Without a device: Print this lesson, use paper cards or the supplied fictional text, and discuss the checks in pairs. A student can later enter their own notebook record for teacher review when a device is available.
Notebook: write your corrected or unresolved conclusion, the evidence you actually checked, and a reflection. Do not include passwords, identity documents or private information. Original BrainCheck companion content, BCAI-v1.