It is a common complaint among teachers that students forget what they have learned soon after taking a test. The phenomenon is seen in both secondary and undergraduate chemistry courses. This study examines the length of time after a test that students in three different chemistry courses (undergraduate nursing, nonscience majors, and high school honors) are able to successfully answer the same free response achievement questions that were on the test. Overall effects on achievement were found to be nonsignificant, as were interaction effects of time interval and logical reasoning level. However, a differential effect between courses on achievement was found, leading to the conclusion that students enrolled in courses in which the continued spiral use of chemistry concepts is not evident, frequent quizzing opportunities are not provided, and a final exam is not given experience a significant decrease in achievement during the first 48 h following a test. This decrease remains constant for at least 2 weeks. Students enrolled in courses in which the spiral use of chemistry concepts is more explicit and regular quizzing opportunities and comprehensive final exams are given did not show a significant decrease in achievement from the original testing to delayed quizzing occasions over a 17-day period.