Quarantine class got a whole lot better for some 1st graders in Georgia this week ... 'cause Shaquille O'Neal popped in their video lesson to say hi -- and everyone freaked out!! TMZ Sports has learned the Big Diesel is a family friend of a student at East Lake Elementary in McDonough, GA ... and with the kids in isolation over coronavirus fears, Shaq decided to brighten their day. The students were doing a lesson over FaceTime ... when O'Neal shockingly popped up on the screen.