Assessment for learning means using evidence of pupils' understanding in the moment to adapt your teaching. The headline tool is the hinge question: a single, well-designed question — usually multiple choice — placed at a critical decision point in the lesson. Pupil responses tell you whether to move on, reteach, or branch into intervention.
Mini-whiteboards are a teacher's best friend. Every pupil writes their answer; on your signal, all whiteboards go up at once. In three seconds you have a full picture of who understands and who doesn't — invisible to anyone except you. Compare this to asking 'does everyone understand?' — which produces no useful information at all.