The 1989 meta-analysis reviewed research dating as far back as the 1930s; the 2006 study reviewed research from 1987 to 2003.
Commenting on studies that attempted to examine the causal relationship between homework and student achievement by comparing experimental (homework) and control (no homework) groups, Cooper, Robinson, and Patall (2006) noted, With only rare exceptions, the relationship between the amount of homework students do and their achievement outcomes was found to be positive and statistically significant.
Note: This figure describes the eight major research syntheses on the effects of homework published from 1983 to 2006 that provide the basis for the analysis in this article.
The Cooper (1989a) study included more than 100 empirical research reports, and the Cooper, Robinson, and Patall (2006) study included about 50 empirical research reports.
To be clear, being data or research-based isn’t anywhere close to fool-proof.
So many of the modern trends and innovations that are “not grounded in research,” or don’t “have the data to support them” suffer here not because of a lack of possibility, potential, or design, but because of research and data itself being sluggish in their own study and performance.
Among his most frequently quoted ‘products’ is the Marzano 9–9 instructional strategies that have been proven by research to ‘work’ by yielding gains in student achievement.