Gutierrez, R., & Slavin, R. E. (1992)

A nongraded elementary program is one in which children are flexibly grouped according to performance level, not age, and proceed through the elementary school at their own rates. Popular in the 1950s, 1960s, and early 1970s, the nongraded plan is returning today. This article reviews research on the achievement effects of nongraded organization. Results indicated consistent positive achievement effects of simple forms of nongrading generally developed early: cross-grade grouping for one subject (median ES = + .46) and cross-grade grouping for many subjects (median ES = + .34). Forms of nongrading making extensive use of individualization were less consistently successful (median ES = +.02). Studies of Individually Guided Education (IGE), which used nongrading and individualization, also produced inconsistent effects (median ES = + .11). The article concludes that nongraded organization can have a positive impact on student achievement if cross-age grouping is used to allow teachers to provide more direct instruction to students but not if it is used as a framework for individualized instruction.

Kulik C-L.C & Kulik J.A. (1982)

This article reports results from a meta-analysis of findings from 52 studies of ability grouping carried out in secondary schools. In the typical study the benefits of ability grouping were small but significant on achievement examinations-an average increase of one tenth standard deviations on examination scores, or an increase from the 50th to the 54th percentile for the typical student in a grouped class. The size of achievement effect differed in different types of studies of grouping however. Studies in which high ability students received enriched instruction in honors classes produced especially clear effects, for example, while studies of average and below average students produced near-zero effects. The benefits of grouping were also clear in the area of student attitudes towards the subjects they were studying than did students in ungrouped classes.

Kulik C-L.C & Kulik J.A. (1984)

A meta-analysis of finding from 31 separate studies showed that ability grouping has significant positive effects on the academic performance of elementary school children. The benefits of grouping tended to be small in the typical study of achievement-an increase from the 50th to the 58th percentile for the typical student in a grouped class. One subgroup of studies however produced especially clear effects. In this type of study students of high ability or gifted students were put into special classes in which they received enriched instruction. Studies of this type usually reported significant results and usually reported effects on achievement were moderate in size. Meta-analysis also showed that ability grouping has trivially small effects on the self-concepts of elementary school pupils.

Lou, Y., Abrami, P. C., Spence, J. C., Poulsen, C., Chambers, B., & d’Apollonia, S. (1996)

The effects of within-class grouping on student achievement and other outcomes were quantitatively integrated using two sets of study findings. The first set included 145 effect sizes and explored the effects of grouping versus no grouping on several outcomes. Overall, the average achievement effect size was +0.17, favoring small-group learning. The second set included 20 effect sizes which directly compared the achievement effects of homogeneous versus heterogeneous ability grouping. Overall, the results favored homogeneous grouping; the average effect size was +0.12. The variability in both sets of study findings was heterogeneous, and the effects were explored further. To be maximally effective, within-class grouping practices require the adaptation of instruction methods and materials for small-group learning.

Puzio, K., & Colby, G. (2010)

Although some literacy researchers consider grouping students for reading instruction to be a proven educational practice, the support for this belief is lacking from a research synthesis perspective. With this idea in mind, Slavin comments in the middle of his review on the effects of grouping: "there is not enough research on within-class ability grouping in reading to permit any conclusions" (Slavin, 1987, p. 320). Because of this, the question of whether "and" how to group students is often cast and answered ideologically rather than empirically. This review attempts to see if the empirical research available can answer either or both of these questions. It will contribute to the literacy field by focusing specifically on reading outcomes for classroom teachers, who instruct a wide variety of students. Informed by previous research on within-class grouping, the following three research questions guide the present study: (1) To what extent does within-class grouping impact student achievement in reading?; (2) For which grade(s) or which students is within-class grouping most or least beneficial?; and (3) Do any moderators, especially those identified by previous research (measurement source, teacher development, and grouping type), help explain this effect?

Slavin, R. E. (1990)

This article reviews research on the effect of ability grouping on the achievement of secondary students. Six randomized experiments, 9 matched experiments and 14 correlational studies compared ability grouping to heterogeneous plans over periods of from one semester to 5 years. Overall, achievement effects were found to be essentially zero at all grade levels although there is much more evidence regarding Grades 7-9 and 10-12. Results were similar for all subjects except social studies, for which there was a trend favouring heterogeneous placement. Results were close to zero for students of all levels of prior performance. This finding contrasts with those of studies comparing the achievement of students in different tracks, which generally find positive effects of ability grouping for high achievers and negative effects for low achievers, and these contrasting findings are reconciled.