Well, as quiet and sam already said, you cannot categorise people in only these three categories. Taking into account only how much of studying a student does there still need to be more categories. A student who studies a lot is not necessarily a nerd. This term is used for people who do nothing but studying like their life consists only of it and oftentimes bugger others for not studying. Students with high grades might not be nerds but geniuses or people who somehow manage to include everything in their life, like sports, studying, getting out with friends, social activities, etc...
Amidst the ruins of the ancient city I stand now baffled by the blazing battle fought in front of my bare eyes... oh man how much anime did I watch last night!