It looks like an impressive collection. Note, though, that the games are not actually hosted at the site. The games are described and then linked to through Spree. So it’s possible that a number of the individual games might be blocked by the often bizarre algorithms used by our schools’ Internet content filters.
I’m adding Spree to The Best Collections Of Online Educational Games. However, most, though not all, of the collections there have all their games hosted on one site. I primarily view these sites as useful for students to use when there are a few minutes left in the computer lab and teachers can just send students to one site (that is unlikely to be blocked) to play games of their choice. It can be a little frustrating to them when some are blocked and some are not.