I assume you are talking about the long jump? That's a pretty good long jump for a 10th grader. Without seeing him jump in person it's impossible to say how much improvement he could expect but another foot or two could be within reason. Yes there is more he could probably do with training, but it depends on how knowledgeable his coach is. Is he fast? How many steps did he run from? How's his running form? Was he wearing spikes? Does his coach know how to teach a penultimate step? How was his landing? Did he drop his feet early?
Most first time jumpers get no height off the board and drop their feet early. Another 6 inches of height off the board could give him somewhere around 18 inches of distance (this is where the penultimate step mentioned above comes in). Keeping his feet up and reaching before the landing could give him another 6-12 inches, possibly more. If his run was short, backing up and starting from farther away could give him some more distance, but only if he can still get some height off the board. It's not unreasonable for a 10th grader to run from 8 lefts (or rights) for 16 strides total for each jump.
He could already be maxed out or in the hands of the right coach he could be a 22-23 foot long jumper within a year. 22 feet as a junior used to be the magic mark to get recruited by a D1 college, though some are looking for 23 feet now. If he could learn to high jump or triple jump he would be an even better college prospect. He might have a better shot at that than playing baseball in college!