This was in my schoolyard in Braintree, MA. Its acorns were rather large and came in either shades of green or brown. I couldn't get a single acorn with the top attached to it as most of the tops were still attached to the tree. This is probably a hybrid of some kind.
White oak family, not quite A Swamp white oak leaf... add quercus michauxii.... as a guess
This message was edited Sep 27, 2015 12:09 PM
Are you going back to your schoolyard?
If so, get some more pics - clear, please. Especially the trunk and bark, because I think that will be the sure-fire giveaway to ID this one.
I think you have a Chestnut Oak there - Quercus montana (though some call it Quercus prinus).
You separate this White Oak group species from most all the rest by its Red Oak-like bark, which is ridged/furrowed rather than flaky/peeling like most White Oak group species.
The single leaf you've shown will never be a good way to separate this species from the two that kittriana mentioned - Quercus bicolor and Quercus michauxii - and to which I will add Quercus muehlenbergii. These can have remarkably similar leaf morphology, just to add to the consternation of nascent IDers.
Snap a branch off this tree, and take it where you can get as clear an image as that one acorn. Take pictures of top and bottom of leaf surfaces; buds, acorns, acorn caps, twigs, etc. Get some clear bark shots of the trunk, and maybe an upshot into the canopy. With years of looking up at trees, you will start sorting some of them out just by that aspect alone.
You can also check against the handy-dandy US Forest Service document on oaks: Field Guide to Native Oaks of Eastern North America. This one is on page 66.
http://www.fs.fed.us/foresthealth/technology/pdfs/fieldguide.pdf
