word order - Passive sentences: placing an adverbial before or after the agent

This homework was done by Vasya at school.

Or

This homework was done at school by Vasya.

Are both sentences grammatical? Is it okay to put the adverbial at school either before or after the agent Vasya? (Leaving out the obivous issue of the shift of focus).

I've read that adverbs of manner, place and time usually go in end position, but here the adverbial can possibly be used in either of the two slots.

One person, however, said that her teacher had told her to always place the agent at the very end of a passive sentence (as in my example sentence 2). That made me curious.

Which of the two sentences will look more natural to the native speaker?

Answer

Both sentences are grammatical. Even in the link, Swan's grammar book says "usually go in the end position" (emphasis mine).

Of course, the most natural way is

Vasya did this homework at school. :)

The passive doesn't seem all that natural to describe or talk about such an everyday situation.

But since you asked, the first one

This homework was done by Vasya at school.

seems more generic and therefore natural than

This homework was done at school by Vasya.

I have not bolded at school as in your originals, because in either sentence one can stress either Vasya or at school, or both, at least when talking.

In writing, the term that comes first (Vasya or at school) seems to get more stress if read without deliberately stressing a word.