My son is riding to middle school daily, which is great...

The problem is what to do with his helmet, to protect it?

We left it with him for a few days, he attached it to the outside of
his backpack that he carried through-out the day. At the end of a week
it is all dented and cracked in places (the foam is fragile by design)
- it will need replacing. I cannot afford to replace his helmet every
couple of weeks or so...

I cannot fault him, it is just the nature of being a kid, the fact it
is on the outside of the backpack and the abuse the backpacks get when
left outside for PE.

There is no room inside the backpack - full of required binders, etc...

Several kids cable the helmet to their bikes, but I have seen the same
abuse and more - kids kicking them, stepping on them, bumping them
with backpacks and other bikes...

The solution I came up with was:
I have been riding with him anyways, I just take the helmet back with
me... But this leaves him dependent on me to bring the helmet and I am
sure there will be a time I cannot meet him, or he will not want me
riding with him...

Ideally I would like him to carry his helmet with him.

Is there something that can help protect the helmets?
Is there a helmet carrier available?
Can anyone think of another solution?

- Scott