This report describes a study of the effects of using pretests in science classes on chapter test achievement results. The targeted population consisted of eighth grade science students at a junior high school from 1992 to 2001. Whether giving a pretest followed by a posttest at the end of the chapter, or giving only the test at chapter end resulted in superior class averages was investigated. Results show that in all cases giving pretests increased the score on the posttest over the use of the posttest only. A statistical analysis was performed to detect any difference in science test averages for the targeted groups. In three subject areas (Genetics, Chemical Families, and Rocks and Minerals), the null hypothesis was rejected; giving a pretest did increase achievement. For one additional topic, the null hypothesis was supported; the pretest did not increase the achievement score in comparison with the results from posttest alone. It is recommended that the use of the pretest/posttest format be followed, with the objective being a positive effect on student achievement as measured by the Illinois Goals Assessment Test. (Contains 11 tables and 23 references.) (Author/SLD)