Swallows and Amazons?
The Lion, the Witch and the Wardrobe (peter as leader)
...
Percy Jackson
Artemis Fowl (maybe, just check it's a male leader)
Swallows and Amazons (series). I thought of that too. But the "leadership" isn't really clear.
The Lion, The Witch. I thought of that too, and sort of discounted it. Perhaps Prince Caspian in the two books. Or even Puddleglum. But not really much of a leadership example.
Percy Jackson: Again he's technically the leader, but like the other two, any "leadership" is more about structure and quite unimportant really to the story.
Oddly, Artemis Fowl, the criminal Mastermind teenager is a leader of sorts. He has his faithful butler, Mr Butler, and Butler's niece. In a crazy manner he is more a "leader" (planning, giving orders, plotting etc) than the others. I've only read the first book (which is crazy, but I rate it better than Darren Shan, but I only read one of them, the 2nd) and found the evil criminal mastermind teenager less obnoxious and the book better than I expected. But I'll not be buying (or leading) any Artemis Fowl or Darren Shan books to my grandchildren. I read all sorts of stuff for "research" purposes. Neither (nor Percy Jackson) comes close to the Arthur Ransome series starting with Swallows and Amazons (I have all of them).
Dune is definitely very adult!
None of the books except
maybe Prince Caspian (the book, and I'm doubtful) have any significant useful Leadership Role models I think. Or possibly Puddleglum in the Silver Chair, but he is a very untypical sort of leader.
Aragorn?
Polgara in Eddings? (a woman)