A multiple baseline design across participants was used to determine how teacher greetings affected on-task behavior of 3 middle school students with problem behaviors. Momentary time sampling was used to measure on-task behavior during the first 10 min of class. Teacher greetings produced increases in students' on-task behavior from a mean of 45% in baseline to a mean of 72% during the intervention phase. Teacher greetings represent an antecedent manipulation that can easily be implemented in classrooms to improve students' on-task behavior. (Contains 1 figure.)