This app was mentioned in 2 comments, with an average of 3.50 upvotes
InMind VR is a brain themed shooter, calling it educational is quite a stretch, and the representation would make a neurologist cringe.
Stellar Dive Experience VR allows visiting different planets, but it isn't scientific either and requires a gamepad to move around. (18min YouTube video)
Something already usable in class would be the [VR street view mode](/r/GoogleCardboard/comments/2qzm40/apps_with_the_wow_factor/cnb23b2) in the Android Maps app.
Solar System can display planets within the room you are standing in, if you can get it to work on your phone.
Expeditions is a cooperation between Google and several traditional providers of educational content, but it isn't open to the public yet and focusses on (very advanced) guided 360° video group experiences. (7min Verge interview with demos)
A lot of educational material is expected for the new Mattel VR View-Master, coming in October.
This app it's so fuck*ng amazing!!
https://play.google.com/store/apps/details?id=com.Graphinuts.StellarDiveDEMO&hl=es-419
Just use a bluetooth joystick and get adictic to it!!