This study compares the effect of the objectives-based test collections of the Instructional Objectives Exchange (10X) on reading comprehension and word-attack skills of fifth-grade students in a basal reader program. The 10X, a nonprofit educational organization, was established in the late 1960s to provide educators with instructional materials such as criterion-referenced tests to allow realistic assessment of students in reference to specific instructional objectives. The study compares gains in reading comprehension and word-attack skills of a research group with the gains of a control group, using the Stanford Diagnostic Reading Test for both pre-test and post-test. The 10X criterion-referenced tests were added to the reading program for the research group but not for the control group. Of the 121 students, 68 were in the experimental group and 53 in the control group. The two groups were equated by analysis of covariance, using IQ and pre-test scores as the covariates. The findings indicated that the use of 10X criterion-referenced tests as practice material is likely to result in a more significant increase in knowledge of word-attack skills by fifth-grade boys and girls than other published material. However, findings did not indicate superiority of 10X materials similarly used for comprehension skills. (Author/TS)