Essay questions and the effects of their use on student scores are examined by a teacher through collaborative action research. Collaboration with the teacher's graduate school faculty resulted in refinements to the research question and development of a practical study methodology. During the two years of the study, the teacher taught four science classes of college-bound high school students of average and above average ability and four classes of science for vocational students of average and below average academic ability. In any one term, he would use essay questions in two classes and not use them in the other two. A total of 77 college-bound students and 97 vocational students completed the study. In general, essay questions, when used, accounted for about 25% of the overall test score. Time of day the class was held had no effect on student achievement, and, as expected, the classes that took the same textbook-supplied objective tests had similar average scores and attitudes about testing. When essay tests were used, the college-bound students' test scores went up almost 10% overall, with increased interest in studying for tests and increased motivation for learning the material. In the vocational group, the overall average test scores decreased by over 10%, with 5 students decreasing their scores for every one that increased his or her score. Students expressed dislike for the essay questions and tended to leave them unanswered. Additional research is necessary regarding the use of essay questions with below-average students. (Contains 51 references.) (SLD)