Can you spoil the ending in a book report?

No. I have always been told by my teachers that you arent suppose to ruin the ending. The point of a book report (besides to get a grade) is to tell about the book you read and to make it seem like the most interesting book ever. Your suppose to end in a way that leaves everyone that read your book report guessing about the ending and that makes them want to run out and read the book.

A book report HAS to spoil the ending, because it tells what the book is about. If you leave out the ending, no one is going to believe you read the whole book.

A book REVIEW, on the other hand, never tells the ending. It can refer to the characters, to some of the problems, to the climax - but not give away the ending.

Yes, because more often than not the teacher wants you to explore the various themes & imagery in the books. The ending is a resolution to all of that, so it's pretty important to include it.

If all else fails, ask the teacher!

Yes, that's usually how a teacher sees you read the whole thing.

Unless it's a report you'll have to say in front of the class, then not so much.