Northwestern has a winning formula for academic prep. There are "free agents" or self-preppers who attend there without being sponsored by an academy. Historically, they have a big percentage of Falcon scholars. They also have students sponsored similarly by other SAs. Their program is comprised of structured academics and physical fitness for a semester, including taking the SAT and ACT up to two times. SAT typically improves 70-100 points and ACT improves 2-4 points. The physical fitness helps to improve CFA scores. All these things are geared to improve the WCS for re-applying to SA. For the second semester you attend any college you'd like and take English, Calculus, Chemistry and Physics. During the Fall, students apply to SAs, including competing for nominations from rep or senator back home. It is a great program, and our son strongly considered it as an option before the FFS offer arrived. You can call NWP and ask what their academy appointment success rate has historically been for self-preppers. I seem to recall reading it was somewhere around 2 out of 3, but I don't remember where I saw that. I suspect one of this year's alums will be able to offer their perspective on number of successful free agents from this year's class.
Attending community college or even a state school and demonstrating academic success, improving CFA and SAT/ACT on his own is also a good option, especially if he's involved in something that helps demonstrate leadership. ROTC is a plus since it shows his commitment and desire to be an officer.
Both options will help improve quantitative factors in the selection process. There's also a perseverance factor that comes from reapplying. His essays and interviews are avenues to describe the qualitative factors and ultimately show why he is a stronger candidate for c/o 2026.
NWP is a great choice since he would be surrounded by people sharing similar goals and their program is well structured. If he's self-motivated and has the drive and focus, then the local college plus ROTC route is also a great option.