If I remember, say, algebra class, the kids who did best were mostly kids who found algebra easy. Somehow it just made sense to them, and the concepts clicked with them as soon as they were introduced. If you praised them for putting in effort, would that be believable? Maybe it's different in classes which are heavy on memorization, but that was my experience in concept-heavy classes; the best students just got stuff instantly, and subjectively felt it to be nearly effortless.
Certainly in my own strengths/weaknesses, I felt that I put in the least effort in the classes I did best in. Where I put in more effort was stuff I wasn't as good at. Praising me for that might've been believable, but if someone praised me for putting in effort in the stuff I was really good at, my reaction would've been sort of incredulous, since I hadn't done so. Not consciously as "effort", anyway; though it's plausible there are things I did in my spare time as "fun" that shaped what I was good at (like puttering around with computers, and reading a lot of books).
Before someone mentions the "local library", there was none during my high school years. The closest one (in the next town over) specifically barred people from my town from using it (taxes and another less happy social reason).