First contribution. Feedback gratefully received :) When introducing new topics in mathematics, the teacher could write out a series of problems and questions on ‘challenge cards’ for use as an extension activity in lessons. Pupils simply take one of the cards (perhaps from a ‘challenge box’), attempt the problem, and then move on to the next challenge. To extend this further, confident pupils could be issued with blank ‘challenge cards’ so that they can design mathematics problems for their peers.