The Benchmarks for Science Literacy and the National Science Education Standards strongly suggest that students should be engaged in hands-on learning. However, from many corners, the original "mental training" rationale for school labs has been criticized, the "cookbook" nature of laboratory exercises condemned, and the prevalence of using laboratories simply to verify previous classroom content questioned. These attacks are justified. Too frequently the school laboratory is far removed from the recommendations of constructivist teaching and is at odds with the way scientists themselves investigate problems. In order to enhance and revitalize laboratory teaching, one must recognize that not all laboratory activities have the same impact on learners. The cognitive component of the exercise is one of the most potent variables worth considering in predicting how a given activity will affect students and what learning it might foster. Here the author presents a number of suggestions that will enhance the overall student laboratory experience.