"Test preparation" activities can range from simple practice to in-depth instruction, but most of these activities use some form of test familiarization, drill and practice with feedback, training in strategies for specific item types, and general test-taking, subject-matter review, and skill development exercises. Two experiments were conducted to study the effects of test preparation on results from the American College Testing program (ACT) Assessment. In the first experiment, a random sample of 10% was selected from one students who took the ACT between October 1, 1994 and September 20, 1995 (69,251 students). These students had answered test preparation questions as part of the information they supplied for the ACT. Gender, ethnic/racial, and family income differences in test preparation were also examined. Almost half of the students had engaged in some form of test preparation, with lower income and minority students reporting engaging in combinations of activities more than other student groups. The types of test preparation studied had little impact on student performance, with only practice tests showing a positive, although small, impact. The second study considered students who had taken the ACT more than once in the time period of the previous study. The sample consisted of 126,253 repeaters. The same information was obtained and the same analyses performed. Over half of these repeat test takers engaged in some type of test preparation before the second ACT, but results suggest that test preparation activities have only a minimal impact on increasing the second ACT Assessment scores beyond gains from simply retaking the test. Results overall suggest that test preparation activities have little impact on scores. (Contains six tables and eight references.) (SLD)