An Exercise Box is a box that you can have in class in which you put exercises that the students design for each other. Each class can have its own Exercise Box which can be a small cardboard box or shoe box with cardboard dividers. This, ideally, should be kept in the classroom or taken to every lesson.
Students can learn a great deal by designing exercises.
Instead of asking students to do an exercise for homework, you can ask them to make one. You can check through a student-designed exercise to ensure that it is correct. Students can write a neat, correct version of their exercise on a blank postcard which they can put into the box. They should put the answers on the back. Students can take an exercise from the box if they finish a task before the others or if they find the other class work too difficult.