JK Rowling revealed1 on twitter that Newt Scamander got expelled from Hogwarts.
Dumbledore was a young teacher at the time Newt was expelled. He wasn't able to revoke expulsions.
Yet we know from Fantastic Beasts and Where to Find Them2 that Newt had graduated Hogwarts:
Upon graduation from Hogwarts School of Witchcraft and Wizardry, Mr. Scamander joined the Ministry of Magic in the Department for the Regulation and Control of Magical Creatures.
(Fantastic Beasts and Where to Find Them - About the Author)
There really should be no way to miss that fact considering how J.K. Rowling's lawyer has said (under oath) that this is a small book.
For example, the evidence will show that there are 274 entries in the Lexicon pulled from Ms. Rowling's 64-page Quidditch Through The Ages book. I'm holding it up, your Honor. It is not a very big book and they have 274 entries about it alone. Similarly, in her 63-page book, Fantastic Beasts and Where To Find Them, there are 222 Lexicon entries pulled from this book.
(Warner Bros. vs RDR Books, Day 1, Opening - Ms. Cendali)
How did Newt Scamander graduate from Hogwarts if he got expelled?
1 In as much that the movie isn't a reliable canon source.
2 The book, not the movie. (Nothing about this question concerns the movie.)