The results cited in the article suggest that either the answer is yes, or in fact "marginal students" are perfectly capable students who were being passed over.

The text of the article further suggests that many of the students who scored well on qualifying exams weren't taking the classes because they didn't have the parental involvement or default assumption that they would take it.

(Note that the opt-out group was selected from the general population based on the results of an exam; it wasn't a population-wide opt out. I suspect from your comment you didn't see that?)