The following is an excerpt from my book, "Access at the crossroads" described int he left-hand column.
Several reasons are possible why analysis of developmental courses sometimes yields mixed or negative results. As stated earlier about remedial courses, it is unreasonable to expect that years of inadequate education or ineffective student effort in high school can be overcome by a single developmental course. A second reason may be a basic flaw in research design. Previous national studies (Bailey, 2009; Kulik, Kulik, and Schwalb, 1983; Roueche and Roueche, 1993, 1999) did not add variables to their analyses concerning attributes of the developmental courses and contexts in which they were offered. They did not have the ability to sort out poorly managed, average, or well-managed programs. When student data from all institutions are aggregated, it is not surprising to find inconclusive results. A finer level of analysis is needed for this complex issue. The only national study on developmental courses was sponsored through the Exxon Foundation in the late 1980s; it found these courses effective when they observed best practices and poor results for those that did not (Boylan, Bonham, and Bliss, 1994).
The bottom line is that more careful and detailed research is needed to understand developmental courses and the variables that affect their effectiveness. Proponents and opponents of developmental courses call for more research in this area (Bailey, 2009; Boylan, Saxon, Bonham, and Parks, 1993). As the most vexing and controversial element of learning assistance, this issue demands careful and detailed national study. It is one of the recommendations for action listed in the final chapter of this report.