From the academic side, since MMI is an accredited two-year college, all the courses are transferable to a bachelor's degree. The courses taught at MMI, besides the SAT/ACT prep courses, are not designed for prep but for university level work. On the leadership side, every student at MMI is a member of the corps of cadets, so military regimen and leadership opportunities translate directly to the academy life. The final point is that MMI is a prep school for CGAS, so we have personal contact with many people in the admissions department, including having the director of admissions visit MMI at least twice per year.
Ok, sales pitch done. Can a reapplicant get in without going to a dedicated prep school? Yes, they can. Demonstrating success in university level courses is a definate plus that admissions looks at, as well as showing dedication for reapplying. Plus, the farther they go through the four year program, alternative programs come into play. Success at the local community college is good as well, as long as the courses parallel the course work at the academy. That means taking composition, one or two lab based sciences, and the highest level math they qualify for.
Dedicated prep schools can and do improve academic skills, and do an excellent job at preparing a student for the academy. Check, though, that the courses give college credit, or offer a way to get college credit.
Best of luck to all.