The purpose of this study was to statistically evaluate the influence of student placement at reading level by means of an informal reading inventory in one kind of elementary science materials. The materials were used in 21 fifth grade classrooms in four Oregon school districts. The classes were divided into three treatment groups which were distributed among the schools. Treatment 1 consisted of students who read at one of five levels as determined by an individual formal reading inventory. Treatment 2 students read at one of five levels as determined by a group informal reading inventory. Treatment 3 students read at only the middle level of the five levels supplied by the publishers. Analysis of variance revealed no significant differences in achievement on criterion tests items among the treatment groups. The results indicate that the informal reading inventory will place students 1.3 years lower in the materials used in this study than would the Metropolitan Reading Achievement tests. Data on teacher rating indicated that teacher effectiveness was a valid area for further research. (BR)