Coaches usually have a sense of who will pass a preread (and don’t submit those they think won’t pass), so I would guess that most kids do pass their prereads.
I suspect others’ experiences won’t necessarily apply to your student, as grades, the sport, the talent level etc varies. But to answer your question, my son passed all 5 of his prereads, only needed a writing sample for Williams, got his UAA offer in May. The only non nescac he had a preread at can do them before July.