He good at/in English.
Can either preposition be used? If so. what is the difference in meaning?
Thanks in advance.
I'm not sure there's no difference; there's certainly a difference in usage. For example, someone is good at tying knots. Usually, you can use either when referring to something you do in school though.
But even there, I detect a slight difference in meaning.
'John is good at history. Whenever there's a test, I know he'll do well. He's attentive in class, and always does his homework..'
'John is good in history. He has consistently achieved marks of above 17/20.'