This document discusses stimulus variation, which is the skillful changing of stimuli by a teacher to maintain student attention and participation. Maintaining stimulus variation is important for drawing and holding student attention, increasing memory and knowledge retention, encouraging student participation, promoting effective learning, and enhancing academic achievement. Some ways for teachers to vary stimuli include changing voice modulation, using charts/models/specimens, varying facial expressions and body gestures, incorporating demonstrations/activities, varying questioning techniques, and switching between oral and visual presentation styles. The document provides examples of how a teacher might vary stimuli when teaching about the topic of amoeba fission.