In this study, the author examined how attendance in the lab is associated with students' lab grades and overall course grades in an introductory biology course. Results from this study indicate that academic motivation, as expressed by high rates of class attendance, is critical to students' success in introductory science courses. The highest levels of academic performance are strongly associated with attendance, both in lecture as well as in lab. Similarly, poor attendance usually forecasts low grades. (Contains 3 tables and 3 resources.)