The handful of studies that compare corequisite remediation directly to no remediation at all reach mixed conclusions. A Tennessee study found that corequisite remediation in math and English had no detectable advantage over direct enrollment without remediation. In fact, for students in the college algebra pathway, students placed into corequisite support were 16 percentage points less likely to pass college algebra than similar students receiving no remedial support. A more recent Texas study reached a different conclusion: Students assigned to corequisite math were 12 percentage points more likely to pass college math within a year than students assigned to no remediation. The Texas study did not distinguish the types of math courses, so the degree to which the effect was driven by math pathway reforms is unclear. That is, students may be completing gateway math at higher rates partly because they were taking different, less demanding courses, not because the corequisite support made them more proficient.
We know what is harmful, but we have not figured out what is genuinely effective. Part of the answer may lie in design. Corequisite remediation is not a monolithic model, and studies from Colorado and Texas have linked design features such as support intensity and instructor assignment to gateway course-passing rates. These associations may vary by student race/ethnicity, subject, and level of precollege preparation. But much of this scholarship is descriptive, and most of it compares corequisite implementations to prerequisite remediation, making it difficult to tell whether the observed variation reflects differences in how much harm prerequisites cause or in how much help corequisites provide. Sorting that out is the next step.