In popular Chinese language, especially in Internet Chinese language, we use the word "学霸" (literally meaning "academic overlord") to refer to someone who does very well in his/her study and who always achieve high grades in exams.
Also, we use another word "学婊" (literally meaning "academic bitch") when we (jokingly, without any malicious meaning) speak of someone who does excellently in his/her study but who likes hiding it from the others, which is their most important difference from "学霸" : for example, if you ask a "学婊" about how he/she feels about the last exam he/she will most probably tell you "Oh it was too hard for me. I really messed it up, and I must get an F this time!" while in fact he/she performed excellently, perhaps much better than most of the others in that exam.
So are there English equivalents for these two Chinese Internet terms? As far as I know, in U.S. the word "curve-wrecker" might take similar meaning to "学霸", and I'm wondering if there is any other alternative word. But for an English counterpart to "学婊", I simply have no idea.
EDIT I think maybe I need to clarify more about the word "学婊". First it is not equivalent to "modesty", although "modesty" can sometimes explain a "学婊"'s behavior. I think maybe the word "sandbagger" in @Avangion's answer in the meaning "downplay or misrepresent one's ability" is by now the closest word, although it might have an overly derogatory tinge.
Generally "学婊" is a teasing/joking word and is rarely used as an insult. And the motivations why a "学婊" downplays his ability or misrepresents performance may be:
1). He/she knows that this exam was super hard and most people do feel bad about it. So when asked about how he/she feels about it, he/she will not tell them the truth that he/she did quite well, so as not to hurt other people's feelings.
2). Out of modesty. And this part may have been hardwired into Chinese cultural genes from ancient times -- showing off is almost always despised in Chinese cultural context, and modesty regarded as a significant virtue.
3). To deceive his/her peer components by downplaying. This is not the usual case, but can happen.
EDIT AGAIN According to JanusBahsJacquet's comment (I failed to find the link), the Wikipedia definition describes it as someone who “pretends not to cram before an exam, then breaks down in hysterics after and gets comforted by everyone, only to appear top of the class when the results are shown”, which I think is a pretty typical and accurate description.