Several pieces of research contradict this theory. The most recent is the report just published by the president’s “What Works Clearinghouse”. It has been applying a stringent set of criteria to the study of a collection of the most heavily used elementary textbook series. Included in their list were Saxon Elementary School Math, Houghton-Mifflin Mathematics and Scott Foresman-Addison Wesley Elementary Mathematics. All were reported as having “no discernable effects” on learning. On the other hand, Everday Mathematics, the most heavily used of the Reform curricula, was rated as having “potentially positive effects”. (What Works Clearinghouse)
A further piece of evidence is a recent research result in which 22 high schools in Washington that had used Core-Plus (a high-school level Standards-based curriculum) were matched with 22 using other books, where the matching included prior mathematics achievement, percent of students from low income families, percent of underrepresented minorities and student enrollment. The pass rate on the mathematics WASL was significantly higher in the Core-Plus schools. For details of the study, see WASLReport.pdf