I completely concur with Dunninla on this one.
AROTC does not have an application process for 3 year scholarships for applicants that are not in high school anymore.
The chance of him receiving a Campus based 3 year Scholarhip when he is starting the ROTC program as a sophomore is as close to zero as you can get. 4 years ago that may have been a different story but not now.
The best he can hope for is to transfer to the school with ROTC, join the battalion as a sophomore and possibly compete for a 2 year scholarship, be aware that he would be competing with cadets that have aleady been in the program for a year.
Many battalions are now requiring cadets that start their sophomore year to complete LTC the summer between their sophomore and junior year, even if they have completed ROTC in their sophomore year. Some battalions may allow the cadet to double up on the MS classes but it seems the trend is moving towards LTC.
LTC is something the cadet would need to apply for as well, and it is not a guarantee they will get a slot. The other issue is that the number of contracts available to each battalion is getting smaller. This means that a battalion may only have 10 contracts to give cadets moving into their junior year, they may have as many as 25 plus cadets to select from. Once they remove the existing scholarship and some SMP cadets that already have contracts there may onl be 6 or 7 contracts left for the 20 cadets competing.
Right now the scholarship is the least of the worries for a cadet that starts their sophomore year, getting the contract to stay in the program is a much bigger issue.
If your son decided to try and start the university that has ROTC as a freshman he is still too late to apply for the scholarship, he would need to start as a non scholarchip/non contracted cadet and then compete for the 3 year scholarship and that's only if the ROTC battalion has any to offer. Starting as a freshman would however give him a better chance competing for the contract.
Best of luck