The purpose of this study was to ascertain the effects of two factors, the data base used for instructional decision making and the structure of instruction, on student achievement. The dependent data were the number of words read correctly by 117 elementary school students on three basal reading passages. Students were rank ordered in two ways: first by the degree of implementation of a technically adequate curriculum-based measurement and evaluation system, and second by the degree of structure in their instructional programs. The top 27 percent were compared to the bottom 27 percent for both variables. The t tests on the mean z scores indicated no difference in achievement due to the structure of instruction. A significant difference was found between high and low implementation groups on one reading passage; differences between scores on two other passages were not significant but were in the same direction, supporting the hypothesis that a high degree of implementation of a technically adequate data system does lead to greater achievement. The discussion addresses implications for teaching practices. (Author)