This study compares the effect of the objectives-based test collections of the Instructional Objectives Exchange on reading comprehension and word-attack skills of fifth-grade students in a basal reader program. The IOX, a non-profit educational organization, was established in the late 1960's to provide educators with instructional materials such as criterion-referenced tests to allow realistic assessment of students in reference to specific instructional objectives. IOX Director James Popham states the Exchange's purpose as encouraging educators throughout the country to use criterion-referenced instructional procedures. 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 IOX criterion-referenced tests were added to the reading program for the research group but were not given the control group.