The authors expanded their study to 10 school districts in North Carolina, and found that putting students in 8th grade algebra has "negative effects among students in the bottom 60% of the prior achievement distribution"
http://papers.nber.org/papers/W18649?utm_campaign=ntw&utm_medium=email&utm_source=ntwAlgebra for 8th Graders: Evidence on its Effects from 10 North
Carolina Districts
by Charles T. Clotfelter, Helen F. Ladd, Jacob L. Vigdor - #18649 (ED PE)
Abstract:
This paper examines the effects of policies that increase the number
of students who take the first course in algebra in 8th grade, rather
than waiting until 9th grade. Extending previous research that
focused on the Charlotte-Mecklenberg school system, we use data for
the 10 largest districts in North Carolina. We identify the effects
of accelerating the timetable for taking algebra by using data on
multiple cohorts grouped by decile of prior achievement and
exploiting the fact that policy-induced shifts in the timing of
algebra occur at different times in different districts to different
deciles of students. The expanded data make it possible to examine
heterogeneity across students in the effect of taking algebra early.
We find negative effects among students in the bottom 60% of the
prior achievement distribution. In addition, we find other sources
of heterogeneity in effects.
