But the study is applicable to students in many other disciplines.
The study is titled "The Critical Importance of Retrieval For Learning" by Jeffrey Karpicke and Henry Roediger, and it's in the February 2008 issue of the journal Science. They examine the question of how best to improve long-term recall. Specifically, they tested whether, once a student can recall a piece of knowledge once, they most improve their long term recall by repeated studying of the material, by repeated testing of the material, or both. Here's the abstract:
So, the takeaway is that the best way to retain (for example), the Black-Scholes option pricing formula isn't to keep going over the formula once you've gotten it down - it's to repeatedly TEST yourself on it. I don't necessarily mean a formal test -- just put the formula on a flash card and periodically (every couple of days at first, but eventually at longer intervals) try to write it out. After that, check your results against the flash card.
Learning is often considered complete when a student can produce the correct answer to a question. In our research, students in one condition learned foreign language vocabulary words in the standard paradigm of repeated study-test trials. In three other conditions, once a student had correctly produced the vocabulary item, it was repeatedly studied but dropped from further testing, repeatedly tested but dropped from further study, or dropped from both study and test. Repeated studying after learning had no effect on delayed recall, but repeated testing produced a large positive effect. In addition, students' predictions of their performance were uncorrelated with actual performance. The results demonstrate the critical role of retrieval practice in consolidating learning and show that even university students seem unaware of this fact.
Of course, if you're studying for the CFA exams, most of the test-prep companies have test banks with numerous questions on each topic, so using them would be perfectly consistent with this approach.
I almost forgot - you can read the Science article here.