This paper offers a summary analysis of 4 years of interviews with 1,003 kindergarten and first through third grade teachers regarding their experience in teaching either a small class, a regular size class, or a regular size class with a full-time teacher's aide. The paper uses teachers' descriptions of their experience to explore the effect of reduced class size or reduced teacher/pupil ratio on developmental appropriateness of primary grade curriculum and on adult-child interaction. Current class size research is briefly sketched. The paucity of findings regarding classroom processes is noted. Next, Project STAR, a 4-year longitudinal study of effects of reduced class size and teacher/pupil ratio in kindergarten through third grades is described. Results of the teacher interviews are summarized and discussed in relation to the National Association for the Education of Young Children's position statements on developmentally appropriate practice in the primary grades. It is concluded that small classes of about 15 students and regular size classes of about 25 students and a full-time aide contribute to a primary grade experience that is more congruent with the developmental and learning needs of students than is the experience of proportionally larger classes. (RH)