Use mini-whiteboards to hear from all thirty at once

Whatever the question (a calculation, a sentence, a labelled sketch), have every student write on a mini-whiteboard and show on cue. You get an instant scan of the room: who has it, who half-has it, and which wrong answer is popular enough to be a teaching point. Wiliam (2011) calls these all-student response systems and places them near the centre of formative assessment done well.

In practice

• "3, 2, 1, show me." Boards up together, so nobody copies and nobody hides.
• Scan for the pattern, not each board: mostly right, move on; split, pairs argue it out; mostly wrong, reteach now, not next week.
• Best-value question type: "Which of these is wrong, and why?" It surfaces reasoning, not just answers.
• No boards? A4 paper in a plastic wallet does the job.