Edited: If 'at academic level' is an adverbial phrase, it wouldn't need an article. Remember that adverbial phrases made up of a preposition and noun phrase generally dispense with the definite article ( as in "by train" "in bed" and so on). So, if you're using 'at academic level' as opposed to another level ( e.g. 'at primary-school level'), it would not need an article. However, you would need the definite article if you're talking about specific academic levels which you've already mentioned or are about to mention ( or are understood from the context). You'd use 'the' if the reference is definite and specific. For example, if it means 'at the [right] academic level [for a given context]' or 'at the [appropriate] academic level [for a particular student]', then the article would be needed.

Su.Ki. ... Always, your humble student... Richard

Thank you for your comment, Richard. I've amended my answer.

Great question! Yes. "The" or "an" is necessary in this case. English has many rules and more exceptions to prepositional phrases such as this. In the end, a native speaker and experience will help you to sound natural.

Adverbial phrase conventions/rules aside, doesn't the phrase "at the (specific) academic level" just sound better because we are specifying a level? Isn't it the function of the article the to determine/denote specific nouns? Here I sit wondering...