A study on the efficacy of ASSISTments, funded by IES and conducted by SRI International, produced reliable gains in student learning. The posttest of the study was McGraw Hill's standardized test called TerraNova that is used by thousands of students. According to McGraw-Hill students normally improve about 11.66 points between the end of one year of middle school and the end of the next. In the study, students using ASSISTments improved an additional 9 points compared to those randomly assigned to the control. This 75% improvement is large, and compared to other proven methods like say raising class size, is extraordinarily cost effective.
Rochelle, J., Feng, M., Murphy, R. & Mason, C. (2016). Online Mathematics Homework Increases Student Achievement. AERA OPEN. DOI: 10.1177/2332858416673968, Oct 2016