Learnt something at or learnt something in?

Question

If I say, I learnt something at 11th grade, is that correct? Or at should be used only when referring to places or particular dates?

Answer 1

"At" here is incorrect. "I learnt something in 11th grade" is correct.

We use at, in, and on fairly arbitrarily depending on what we're referring to. The correct preposition here is in