A study evaluated the validity of the Illinois Goal Assessment Program (IGAP) grade-3 reading assessment from 2 perspectives: its relationship to 21 other measures of reading via factor analyses, and the sensitivity of the IGAP to instruction in 3 schools via multiple regression. Data were collected in a longitudinal study involving 350 students. Factor analyses indicated the tests load on 2 factors, a comprehensive factor and a factor contrasting reading rate/accuracy with narrative comprehension. Two elements of the IGAP failed to load on either factor: the literacy survey or the metacognitive measure. The three regressions models were consistent across sites. After controlling for entering ability, home influences, and grade-1 and grade-2 teachers, instructional activities in grade 3 that focus students' attention on comprehension are associated with higher IGAP scores. Instructional activities that focus students' attention on decoding are associated with lower scores. (Contains 95 references, and 8 tables and 1 figure of data.) (Author/RS)