The effect of grade level on the relationship between class size and academic achievement

The purpose of this investigation was twofold: to study the relationship between class size and academic achievement, and to examine the effect of grade level on this relationship. The sample consisted of 193 groups of students in small and large classes from grades three, six, and eight in the District of Columbia public schools. To control for pupil ability, each school in the sample had between 35 percent and 65 percent of its students scoring above the median grade equivalent consistently from 1985 to 1987. Faculty experience was controlled by requiring all teachers in the respective grades to have between four and twenty years of experience in the teaching field. Scores obtained from the Comprehensive Tests of Basic Skills (C.T.B.S.) in Reading, Language, Math, and Science for the period 1985-1987 (combined years) were used to measure achievement. (Eighth graders were not tested in Science.) The t-test was used to test the null hypothesis of no significant difference between small and large classes in academic achievement. Analysis of Variance tests were conducted to determine whether the relationship between class size and academic achievement was affected by grade level. The results showed statistically significant differences in favor of small classes in grades three and six. The differences at the third grade seemed greater than those at the sixth grade. At the eighth grade level, the analysis found a statistically significant difference only in Language. In general, the hypothesis stating that there is an inverse relationship between class size and academic achievement seems to be supported by the results. With regard to the interaction effects of grade level and class size, the analysis found a statistically significant difference only in Math. Supplementary analysis showed additional differences in the interaction effects by year. However, on the basis of the general findings, the null hypothesis on the interaction effects of grade and class size cannot be rejected.