Tā qǐzhǐ shì gè hǎo xuéshēng, tā hái shì wèi tiāncái.
He is far more than a good student - he's a genius.
Tips
grammar
岂 is a classical rhetorical-question particle ('how could?'). 岂止 = 'how could it stop at?' = 'far more than'. Pattern: 岂止 X，(还/简直) Y - 'not just X, but (even/downright) Y'. Slightly literary register; in casual speech use 不只 instead.
