Baffled

I've finally finished grading the final exams for my Good Book intro and I'm completely baffled.

As I did for the mid-term, I provided a list of topics that would be covered on the final. And I think that the exam questions were clear and fair. I even conducted two review sessions.

And yet, the class averages for my two sections were 64% and 57%. (The highest grade was 94%.)

Did my students simply decide not to study for the final?