The most recent Gadfly published a short review by the Fordham Institute's Amber Winkler of a new Mathematica study (for the U.S. Department of Education's Institute of Education Sciences) of four elementary school math curricula:
If you're looking for a truce in the math wars, this study is not it....The study found that students taught with Saxon Math (published by Saxon) and Math Expressions (published by Houghton-Mifflin) performed significantly better than those taught with Investigations (published by Pearson Scott Foresman) and Scott Foresman-Addison Wesley Mathematics (also published by Pearson Scott Foresman).
Winkler points out that Saxon and Investigations are polar opposites:
Saxon math...is lauded by most traditionalists as the "Open Court" of math, and used in plenty of Catholic schools. On the other hand, the most constructivist math program of the four, Investigations, had the poorest results; this curriculum is described in the report as a "student-centered approach" that "focus[es] on understanding rather than ‘correct answers,'" and in which students "frequently create their own representations."