http://www.ascd.org/ASCD/pdf/journals/ed_lead/el199904_loveless.pdf This is an article from the late 90s about detracking in the name of equity. It discusses some of the studies that have been cited in support of heterogeneous grouping. It also discusses social equity.
A quote from it.
"Students in heterogeneously grouped algebra classes didn't learn as much as students in tracked algebra classes. This held true for all ability levels—high, average, and low. In contrast, when survey courses in math were heterogeneously grouped, low-ability students benefitted. Tracking apparently doesn't affect all math courses identically."
http://www.giftedteam.org/pdf/links/ability_grouping_studies2.pdf This article discusses the various methods of ability grouping and found that if you keep the curriculum the same, there is little difference between achievements of the various ability groups, if you ability group and adjust the curriculum and pace to the group, you have some improvement in achievement in lower and middle groups, and if you offer accelerated material to the higher groups, achievement can grow by 4 years in 3 years of instruction. It discusses some of the studies that have been cited in support of heterogeneous grouping.
http://www.vanderbilt.edu/Peabody/SMPY/InequityInEquity.pdfA 44 page article that makes the case that achievement of average and below average students has been improving while achievement of the above average students has declined, and that this decline is shown in lower scores compared to other countries.
http://www.gifted.uconn.edu/nrcgt/kulik.html"Meta-analytic reviews have already shown that the effects of grouping programs depend on their features. Some grouping programs have little or no effect on students; other programs have moderate effects; and still other programs have large effects. The key distinction is among (a) programs in which all ability groups follow the same curriculum; (b) programs in which all groups follow curricula adjusted to their ability; and (c) programs that make curricular and other adjustments for the special needs of highly talented learners.
Programs that entail only minor adjustment of course content for ability groups usually have little or no effect on student achievement. In some grouping programs, for example, school administrators assign students by test scores and school records to high, middle, and low classes, and they expect all groups to follow the same basic curriculum. The traditional name for this approach is XYZ grouping. Pupils in middle and lower classes in XYZ programs learn the same amount as equivalent pupils do in mixed classes. Students in the top classes in XYZ programs outperform equivalent pupils from mixed classes by about one month on a grade-equivalent scale. Self-esteem of lower aptitude students rises slightly and self-esteem of higher aptitude students drops slightly in XYZ classes.
Grouping programs that entail more substantial adjustment of curriculum to ability have clear positive effects on children. Cross-grade and within-class programs, for example, provide both grouping and curricular adjustment in reading and arithmetic for elementary school pupils. Pupils in such grouping programs outperform equivalent control students from mixed-ability classes by two to three months on a grade-equivalent scale.
Programs of enrichment and acceleration, which usually involve the greatest amount of curricular adjustment, have the largest effects on student learning. In typical evaluation studies, talented students from accelerated classes outperform non-accelerates of the same age and IQ by almost one full year on achievement tests. Talented students from enriched classes outperform initially equivalent students from conventional classes by 4 to 5 months on grade equivalent scales."
