I gather puzzlers and problems from the Internet, middle school math magazines, old textbooks and other publications. Each day, I put a challenging problem on the overhead and give my students time to work on the problem. When I call 'time', I place a small square of tag board on the desks of those who got the correct answer. The students write their names on the squares and place them in a can. I draw out one name and that student has to explain the method he or she used to get the correct answer. The student receives a prize for a good explanation. Then, I ask for other students to share their explanations. The students benefit from having to explain their thinking process and from seeing multiple methods of solving problems. I am amazed at the variety of methods they use to solve problems.