Right away it's unbelievably obvious that they couldn't get extras to make it seem like a real school-year; so they wrote in the scapegoat of "weekend detention". Although that doesn't explain away the construction fences that you can see in the beginning, clear indication that they got in during Summer renovations. Not a bad idea to secure locations, just get the fences out of your shots.
All the characters are 1-dimensional, with each of them representing a cliche clique in schools. They try to come together, but it seems forced and superficial. You really don't care about any of them, because the characters are either unlikable, or the 'nice ones' never seem like they're really in danger. The one and only faculty member isn't any less of a stereotype.
At one point the director opted to skip the music and let the terror of the haunting try to hold suspense on it's own. It failed. Hard.
At this point Blumhouse/Into the Dark is just giving us monthly classes on how NOT to make horror movies. Get some friends drinking and have a laugh at the incongruities of these, and just enjoy yourselves :)