Wow, that's an awesome experience. We were lucky and when DS was in 7th grade we attended a Service Academy Forum. The state West Point Parent club had a signup sheet for future mock nomination interviews. DS put his name on it and lo and behold, he got a call in mid-summer from them inviting him to the mock interviews.
They also, chewed him up and spit him out, gave feedback, and sent him back to the waiting room to regroup. 20 minutes later, he got his Mulligan shot and nailed it. The advice and feedback they provided was key I believe to his success in later interviews.
Also, to reiterate what others have said about 'you have to know someone' or have political alignment to earn a nom, not true. My husband and I actively supported the opponent of two MOCs DS got noms from. And until the nominations were final, he never met, saw, or spoke to the MOC, just their staff.