This is from the new William G. Bowen book, Higher Education in the Digital Age:
…we found no statistically significant differences in standard measures of learning outcomes (pass or completion rates, scores on common final exam questions, and results of a national test of statistical literacy) between students in the traditional classes and students in the hybrid-online format classes…This finding, in and of itself, is not different from the results of many other studies. But it is important to emphasize that the relevant effect coefficients in this study have very small standard errors…what we have here are “quite precisely estimated zeros.” That is, if there had in fact been pronounced differences in outcomes between traditional-format and hybrid-format groups, it is highly likely that we would have found them.
Note also that this finding holds across various subgroups of the basic student population, including students from families with incomes below 50k a year, first-generation college students, non-white students, and students with GPAs below 3.0.
The core report is here.