When Johnnie performs a handstand for Sally, the extras in the background change dramatically: a woman at her locker turns into three people talking and back again.
Jesse parks his van against a wall and Sue Ann joins him inside the van. As Jesse pulls the curtain closed you can see that his van is facing foliage (not a wall.)
As the cheerleaders fight a player with an orange jersey can quickly be seen even though no team wears orange jerseys during the game.
As Johnnie describes his strategy for the car race a cardboard beer holder moves from the hood of the car to the ground and back again.
When Jesse leaves his van to go talk to the girls in their car at the drive-in diner, he shuts his van door, but as he approaches the girls you can see his van door is open.
The reflection of a man is visible in a classroom window and he signals when Laurie should look out the window at Jessie's van.
Jesse holds up a book and asks Laurie if they were asked to read it for tomorrow. The book is "Workbook for Gregg Shorthand for Colleges" (1973 edition) which seems an unlikely assignment for a high school male in the mid 1970s.