Just watched this movie a little while ago. What is the significance of him tossing his grade report into the ocean unopened? That would seem to indicate to me that he was dropping out of law school. Wasn’t Susan divorcing her husband because he dropped out of law school after the first year to go hike around Europe?
I took it mean that Hart had given his all, and was confident that he had succeeded in what he had set out to do. He hadn’t let Kingsfield beat him like Kevin had. Therefore, his grade was irrelevant.
The TV series showing Hart staying in school for the duration answers that partly. It doesn’t answer why Lindsay Wagner never even asked her boyfriend his first name. 
I thought the paper airplane scene was to show Hart retaking control over his own life, not letting Kingsfield dominate him any longer now that the class was over. He didn’t need to know his grade because he knew the old bastard would be fair and he knew he knew the material cold.
TV series that follow from movies have been known to do a little imaginative explaining, so the fact there was a TV series didn’t completely answer the question for me.
The book indicates that Hart got a 93 in Contracts. And its author was in his 3rd year at Harvard Law when he wrote the book. I chose to believe that this indicates Hart did stay in law school - he just realized he wasn’t simply his grade.
To me, the ending indicated that Hart was no longer going to be the stereotypical, overly ambitious, nose-to-the-grindstone grade-grubber he started out as.
Even though we see that he DID get an A in Kingsfield class, Hart’s priorities have changed. At the start of his freshman year, he’d have freaked out at the thought of getting a poor grade. By the end of the movie, he didn’t care.
He was HAPPY and in love now, and that meant more to him than his grades in a class.
Agree with those who saw it as him re-claiming himself. He wasn’t dropping out; he just didn’t need to know his grade.
There is a remarkable symmetry in the last scene.
Susan holds the letter from her father concerning her divorce proceedings, and says “a piece of paper and I’m free”.
Hart the considers his own piece of paper, which in a sense also came from Kingsfield. Is envelope’s contents the beginning or the end of his servitude?
The film’s title becomes perfectly clear at that point, if it hadn’t before.