At their best, giant college classes can be effective and inspiring — a way to get the best teachers in front of the most students. But according to Carl Wieman, who won the 2001 Nobel Prize as a physicist at the University of Colorado, such successes are rare. Students often tune out and are turned off. Charismatic lecturers get good reviews but, the data show, are no more effective than others at making the most important concepts stick. Colorado is one of a number of campuses making significant changes in how at least some large introductory courses are taught and organized.