(About 28:20 in) After David saves Mary and Jane from being raped by Bruce and company in the classroom, Mary's shirt is intact and buttoned up.
The next scene is the three of them exiting the building and Mary's shirt is torn up and disheveled.
Sand on Mark's chest is visible in long shots but vanishes in medium shots while he is on the beach talking to Teresa, right after he has argued with Paul.
After the bullies dump all the books on Arthur in the library, David goes to help clean up and asks Arthur, "What happened? Looks like point six on the Richter Scale." A .6 on the Richter Scale wouldn't even be a minor vibration.
When Bruce falls onto the power-lines in his hang-glider he is electrocuted, but this is impossible unless he is grounded.
The camera is reflected in the car while David is talking to Rodney.
When the van is parked atop the hill, above the beach, a huge boom mic is clearly visible above
No one should expect to get away with painting graffiti in the middle of a busy school day, as Spoony seems to think.