It takes a particular type of person to use the clown's hat as an effective classroom tool. And clearly, it can't be the only method used. That said, I also think that students want to know that their instructor has a soft side - a sense of humor - and knows when to push the class and when to relax a bit. Each student has a different frustration point that changes depending on many variables. How do you monitor your students to know that you have pushed and challenged them as far as you can without frustrating them? Do you focus on the mid-range student? Slower students?