Previously Wellesley had leveling for all of their classes but in 1998 moved to more what we now know is the "middle school model" and eliminated leveling except for math classes. Over time they have come to more of a heterogeneous (mixed) grouping for math as well, however, they maintain accelerated CMP classes for their 8th graders. (Dr. Bach has said that having 50% of the class move at an accelerated pace is not considered to be leveling.)
Wellesley outscored Andover on the MCAS over the past three years, however, their rate of decline is actually steeper than ours.
New update: Wellesley's middle school program of studies for 2007-08 is now published and is quoted below:
"In grade eight, students are heterogeneously grouped for all subjects except Mathematics. In Mathematics, there are four course offerings, a core course in Algebra, an accelerated Algebra course, a course designed for students who would benefit from a measured pace to master the major topics of first year algebra, and The Interactive Mathematics Program.
Teachers will offer their perspectives to parents and seventh grade students for the level placement in eight grade mathematics. After careful consideration by the teacher of a student's work and study habits, classroom performance, and current achievement, an appropriate level placement will be suggested."
(It appears that we were incorrect in saying that Wellesley offers CMP as its sole middle school math curriculum.)