Engaging in explanation while studying expository science texts can improve comprehension. The present study varied the timing of explanation activities and restudy opportunities before taking final comprehension tests on a set of 6 topics studied as part of a course in Introduction to Psychology. When students had the opportunity to restudy in the same session, then comprehension benefited from explanation activities. However, no benefit from explanation activities was seen when they were done in a session prior to the restudy opportunity. [This is online version of paper published in "Preprint Repository for the 32nd Annual Meeting of the Society for Text & Discourse" (No. 9587).]