これは学生の間違いだ。

this (indicating an item near the speaker, the action of the speaker, or the current topic); this person (usu. indicating someone in one's in-group); now; here; I (me); certainly

topic marker particle; indicates contrast with another option (stated or unstated); adds emphasis

student (esp. a university student)

indicates possessive; nominalizes verbs and adjectives; substitutes for "ga" in subordinate phrases; (at sentence-end, falling tone) indicates a confident conclusion; (at sentence-end) indicates emotional emphasis; (at sentence-end, rising tone) indicates question

mistake; error; blunder; accident; mishap; trouble; improper conduct (e.g. between man and woman); indiscretion

be; is; indicates past or completed action; indicates light imperative