The author has been using a method for classroom instruction in which he hands out notes with gaps to students. He makes transparencies of the notes and he lectures using the transparencies. The gaps are filled in with information that is elicited from the students or supplied by the lecturer. Others have used similar methods, usually with large lecture classes. The main goal of the present method is to keep the students interested and learning as the class proceeds. The information that fills the gaps varies from single words to segments of programs or proofs to suggestions of ways to solve problems, including descriptions of algorithms. The method is being tested in the classroom in a variety of courses: to determine objectively whether students learn more when the lecturer uses the experimental method than when using a more traditional method; to estimate the degree of student participation using the various methods; and to compare the students' subjective reaction to being taught using the various methods.