That's MIT. The attached picture is taken from "Technology's War Record" which has a little writeup of the ground school and some general notes on the curriculum. The photo is small and fairly grainy, but the architecture of the place matches well.
It also notes - The First Ground School for Pilots at the Institute opened on May 21, 1917.....The first squadron, composed on twenty-three men...."
Count the heads - 23 in the photos.
Looks like your grandfather was in the first class of pilots graduated at MIT.