An experimental study examined temporal manipulation of presentation speed as instructional design strategy. In a between subject design, an animation of a mechanical system, a pendulum clock, was presented at either normal speed or as highly sped up version. Presentation speed was found to affect distribution of attention and understanding of the clock's functioning. Think aloud protocols were analysed for mentions of clock parts as an attention indicator, and for statements about the functions of crucial clock parts. Verbal reports from the fast condition contained more statements about the weight, which is a central part of the clocks' driving mechanism. Written descriptions of the clock produced after presentation included more correct concepts about the key components in the fast condition. For complex dynamic subject matter at least, temporal manipulation of presentation speed seems to provide instructional designers with a way to increase attention to relevant parts and thereby facilitate understanding. Copyright © 2007 John Wiley & Sons, Ltd.