This Assessment for Learning technique helps students communicate instantly with the teacher. If your students are working in groups, they stack their cups on their desk with one colour showing.
As you walk around the classroom, you can glance at the cups and find out which group needs your help. Red you need to deal with immediately and yellow as soon as possible. And if, for example, most cups show yellow or red you can stop the lesson and sort out any problems.
If you can’t find coloured cups, you can improvise a way to display the colours – for example, make some red, yellow and green cones.