It's basically saying the connection is encrypted, but the server is using an outdated and/or exploitable algorithm. I'd call the school and report the error to their server administrator. They need to reconfigure their encryption to use a stronger key in order to prevent the end user from seeing this error message.
Good on Google for blocking the connection. I know it's a pain in the ass to come across this, but it really says a lot about the extent they're willing to go to protect the integrity of encrypted web traffic.
As
@lookoutawhale suggested, you might be able to work around this error by hopping on another computer (or maybe even your smartphone) and viewing on a different browser.