Is this sentence grammatically correct?

I'm grading my students' English composition test right now and I found one answer seemed to be grammatically wrong!
So I deducted her points but she claims that her sentence is just less common expression - not grammatically incorrect.

Below is her sentence:
"In fact, the average child spends more than four hours in front of a screen each day, engaging in screen entertainment, substituing time that used to be spent for physical activity."

I personally think there should be an 'and' between 'entertainment' and substituiting'.
Also 'that used to be spent FOR physical activity' is what she wrote, but shouldn't it be 'spent ON physical activity'?

I'm just an undergrad student and grading high schoolers' test is my part time job (which means I'm not professional)!
So I might be wrong and her answer might be correct.

If you are a native speaker of English and quite confident in English grammar, please tell me if her answer is correct or not.

If you think her answer is grammatically incorrect, please explain why so that I can convince her.

I agree with Josh.

The sentence also looks OK to me as is. I suppose "on physical activity" sounds a bit better than "for physical activity" to me.

Possibly, the 2nd comma should be omitted. I think that makes the "and" after entertainment less desirable. I think this sentence OK with and without the and.

Actually, I'd recommend:

"In fact, the average child spends more than four hours in front of a screen each day engaging in screen entertainment, time that used to be spent for physical activity."

You substitute one thing for another and spend time on an activity.
What your student means is clear, but her way of expressing it is a little clumsy.

I agree with Guest's recommended solution. If you use substitute it would have to be something along these lines:

" In fact the average child spends more than four hours in front of a screen each day, substituting time that used to be spent on physical activity for time spent on screen entertainment."

W, you wouldn't happen to be German?

No, I'm not German.
Why did you ask that?

Perhaps because what you wrote gives the impression that you might not be a native speaker of English, however the person whose paper you were correcting might be.

From my experience, Germans seem to be the first to "correct" and criticize native English speakers' English. And, no, I am not a native English speaker myself.

I'm neither German nor a native speaker of English. lol

Pavel:

You seem to be a little bit biased toward Germans, no offense intended.

W:

There is no problem with that sentence as far as grammar is concerned. As other people have stated, it does make a hard read.

I would have written that this way:

"In fact, the average child spends more than four hours in front of a screen every day, thus substituting time that was once spent on physical activity for entertainment.

i have a new dilema, would the proper sentence be:

Laura and I are at the store

or

Laura and I am at the store


or would it be Laura and me, are at the store

Laura and me am at the store

It would be Laura and I (therefore We) are at the store