The best way to get a UTR 13 is to either beat several UTR 13s, blow out higher 12s or win 6-7 games vs several 13.5+ or even better a 14+. To play 13.5+s, you basically have to play Future Qualifiers or higher jr ITFs- at ITF grade 4s the highest UTR players might be 13.3ish. Men's opens events have wide ranges from UTR 8-13.5+ but not too many over UTR 13 unless it is an open with big prize money, and some of those have qualifiers (probably for guys under 12.5). Playing Kzoo or National Team prior to Kzoo is another option (you can't register for Nat team-your section chooses team members but you could let USTA section staff know of your interest-often 1-2 alternates end up replacing players who can't attend). Once you get to a UTR 13, it is hard to keep it as those 30 matches roll off in 6 months or less for juniors. Now only do you have to find tournaments with 13+ players, but you have to win big vs other low 12s. If you have 3 setters vs other low 12s, your UTR isnt going to move.
The UTR events on campus can be a good option, but the best players from the host schools may not even play, e.g. the Univ of Mich UTR event was mainly attended by Mich State players who were lower ranked. However most of the Louisville team I think played the Jan Louisville UTR but I believe that was staggered entry so 16 players played in each flight with the top 8 moving up, and the higher Louisville players didnt play until the last flight. I dont know how many low 12s made it into the final flight of 16. Some of the summer circuits have 13+ players-the Mid west and Texas ones had some college players from power schools. In the south, the summer circuits might be 75% juniors.
It is definitely possible to get a 50-70%+ scholarship at some midmajor d1s with your SAT scores and a 12.5+ UTR. Look for teams with smaller rosters than bring in 2 players a year and recruit Americans. They may have a 60/40 or 67/33 split with the higher amount going to the coach's first pick/higher rated player and the lower % to the 2nd. However, even the 2nd player could get 50%+ with 33% athletic and 20%+ merit. With bigger rosters, the $ go down. Encourage your son to aim for 1300 SAT as that jump might bring him a little more academic aid-could be another $1500-2500/yr over an 1150-1250.
Most of the international players playing 1 or 2 at midmajor D1s have some Future Quali experience even if they havent made it to main draw. It is hard for US players as they need to reach their UTR targets by spring or at the latest by late summer after their jr year to get a good offer. Internationals may have taken a gap year or may sign in the summer to play in Jan so they often have 9+ months of experience built into their UTRs even if they are 18, more if they are 19. It is also hard for US players to time it right. Some commit early and play their best tennis their senior year; others wait for the right offer and end up as preferred walk ons on state teams with no athletic $. Private message me if you have more questions. Son played Future Qualis and high nationals and was able to get UTR over 13, but dropped because he didnt beat 12s big enough, and his best wins dropped off in 6 months.Players playing a mix of juniors and adult tourneys have a very hard time playing 30 or less matches in 6 months-many in large sections play 30 matches in 3 months. UTR does not count matches about UTR 3.0 below, but it does count matches 2.0 or 2.5 below and an 0,2 vs a player 2.5 below still cant compare with beating a 1.0+ higher player in straights. Wish UTR would keep a player's best 6 wins in a year and not penalize players for playing frequently. Until they change their algorithm, try to play tourneys with players UTR 1.0 below to 1.5 ahead. Buy a premium UTR membership and use their rating listing option to see the UTRs of players in tournaments you are considering, and then choose the ones that give your son the chance to player some higher players. If your son signs up for ITF Future, he may end up 100+ in alternates, but many players will withdraw before the freeze deadline. It is often worth a gamble to drive to a site and sign in as many alternate to get in the night before the tourney starts.
You said your son does not play well at jr nationals-that is where most of the coaches are and many will make offers right after Kzoo so it may be worth jumping through the hoops playing USTA high level section and nat 2s and 3s to get in Kzoo but it is an expensive process to do all that. It is certainly cheaper to play summer circuits, men's opens, and UTR events which usually take players in order of entry. Also take many unofficial visits spring of your jr year. Dont wait for the free flights in the fall of sr yr-teams may be doing off season unsupervised practices in early Sept so it is harder to get feel for team and coach interaction, and player may have to decide on offer before completing all officials-better to look at favorite schools on your own dime and catch a full practice and match in the spring of jr year.
One last important note-the future circuits will be reduced in 2019 so play this year. 14,000 men and women played Circuits last year, and the ITF wants to reduce the number of pro players to 750 and will create a transition tour that will replace many Futures in 2019. Details on changes arent out yet. US Futures are about 50/50 Hard/Clay-big advantage to Floridians-if you dont get to practice on Clay that limits your options.