After a brief introduction identifying current issues and trends in research on class size, this brochure reviews five recent studies bearing on the relationship of class size to educational effectiveness. Part 1 is a review of two interrelated and highly controversial "meta-analyses" or statistical integrations of research findings on class size, by Gene V. Glass and Mary Lee Smith: "Meta-Analysis of Research on the Relationship of Class Size and Achievement," and "Relationship of Class Size to Classroom Processes, Teacher Satisfaction, and Pupil Affect: A Meta-Analysis." Part 2 reviews "An Experimental Study of the Effects of Class Size," by Stan M. Shapson, from "American Educational Research Journal," (Spring 1980). Part 3 is a review of "Early Childhood Education Classroom Evaluation," by Jane Stallings and others. Part 4 covers "Class Size Project 1980-1981: Final Report," by Andrew T. Carrington and others. Part 5 is a review of "Crowding and Classroom Learning" by David E. Weldon and others, from "Journal of Experimental Education," (Spring 1981). (TE)