Student struggles with the passive

I've been tutoring a Latin student lately. His mother informs me that he's got trouble with the passive. It's not a problem of understanding—he gets the passive in English. It's not a problem of recognition—he recognized passive verbs in Latin. The problem is mapping the Latin passive onto the English structure, and I think I've got the problem nailed down.

Here's a passive sentence in Latin:

Fenestra frangitur.

Here is one way to say that in English:

A window is broken.

Except that's not what any actual English speaker, let alone a 14 year-old English speaker, would say. More like:

A window's broken.

Which is exactly one phonological segment off of:

A window's breakin'.

And I think that's the key. Students hear the progressive (is verb-ing) and some, but enough to screw thing up, passives (is verb-en) as the same thing. So to eliminate the ambiguity they hear, the students kill the tense:

A window was broken.

I could be wrong, but this seems to be the student mistake with present tense passives. Anyone have any insights?

Why so quiet?

Because life. I'm sure I'll get something going here soonish.