Time is the main constraint that I've seen. It is a great thing when there is plenty of it - and there is. Another good thing is when you start a lecture and the next minute (not literally) you turn around and time has run out. This is often the sign of a great lecture, one in which the students were all actively engaged, learning, contributing, and having fun. You know what they say, time flies when you are having fun! But the management of this time is where the art and creativity must kick in on behalf of the instructor. If an instructor is a procrastinator or a last-minute type of person, what is the relationship with that and their true ability to manage time in the classroom?