Information provided by typical and improved conventional classroom achievement tests was compared with information provided by an adaptive test covering the same subject matter. Both tests were administered to over 700 college students in a general biology course. Using the same scoring method, adaptive testing was found to yield substantially more precise estimates of achievement level than the classroom test throughout the entire range of achievment, even in the range where the improved conventional test was designed to be optimal. Adaptive testing also made it possible to reduce the length of the test. An analysis of the effects of expanding an adaptive test item pool indicated that improved precision of measurement could result from the addition of only slightly more discriminating items. A comparison of response pattern information values (observed information) with test information values (theoretical information) showed that the observed information consistently underestimated theoretical information, although the pattern of results from the two procedures was quite similar. It was concluded that the adaptive measurement of classroom achievement results in scores which are less likely to be confounded by errors of measurement and, therefore, are more likely to reflect the true level of achievement. (Author/MV)