Um...I only have one student, and I don't use him much, but he does have a boatload of secrets. hahahaha.
Andrew Diamond (fifth year Gryffindor). He's an orphan but Robert and Kate are his legal guardians. (Wasn't my original plan but he's just evolved that way.) (He's the son of a wealthy, pureblood git who was killed in a bar fight--the same git who killed Andrew's mother. Andrew has a great deal of money but he lives a very 'off the rack' sort of lifestyle.)
He grew up being a pickpocket to survive before he got to Robert, and he prefers climbing to about anything else, and he talks to animals.
But--over his breaks, he's been learning from Michael Tremaine how to be an increasingly proficient burglar. He is finding it easy to 'apprentice' under Michael, and it is not in his best interest for people to find out that he lives with Robert Lupin, nor that he is learning how to be a professional thief. Nor that his father murdered his mother.
That might not be what you're looking to work with---but in student circles, its the best I've got right now. And I'm open to ideas.