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.
Best Answer
Translation is difficult, and translation of slang is even more difficult because of all the non-shared cultural context and nuances involved. So there's usually not a direct translation (one-to-one always) that fits for slang. Often that results in a direct loan word, like 'kow tow' or 'kung fu', or loan translation, like 'brain washing' or 'lose face'. This happens more often than a direct loan because the phonology and culture are so different between English and Chinese.
For these two terms, 学霸 ('school tyrant') and 学婊 ('school whore/bitch') (those are the character for character translations, the nuance of the individual words may or may not be very misleading), there are no such terms for the direct corresponding cultural situation, especially for the second one which seems to be a recent invention. Of course there are terms in the same area of concern (academic excellence):
I'd prefer to have many more terms in that area of which there are many I am sure, I just can't think of them.