Yes that is a possibility in this sort of research design. The exit-test scores are obviously taken as proxy for educational quality and the study cannot test f

Yes that is a possibility in this sort of research design. The exit-test scores are obviously taken as proxy for educational quality and the study cannot test for any "secret sauce" beyond that. On the other hand, there's only so much one can do with observational data doing these sort of causal analyses. I'd say its still an interesting outcome.