Thought I would balance what is being said. My older son played his first year for an ACC university and was pitching against a team from I think the Big 10. He hit 94-97, walked two hit one and was gone.
There is functional velocity and top velocity. There are some who can bench press 300 lbs many times but only top out at 325. There are others who can bench 340 but cannot bench 300 very many times in a row.
What needs to be pushed is functional velocity, not max out out-of-control velocity. My older son was more effective working 88-93, and sometimes the lower reads were 86-87. His functional velocity was pushed up by many good pitchers before him.
Max speed in baseball doesn't mean a lot if it is not functional. However, higher functional speed means domination by a pitcher.
Use of the radar gun will initially push non-functional speeds with many kids. However, after familiarity they will barely notice the gun. A side benefit is later when others gun them, they won't throw to the gun. They'll just pitch.
One other note. I used to believe you always had to work at 80-100% speeds. I no longer believe that. My 11 year old is worked with short-boxing. We throw 1/2 distance to a catcher at low speeds. This is where I work grips, rotation down a line, and dynamic balance and can see his mechanics better. I realized, too late for the older one, that the lower and upper body has to be timed whether throwing slow, medium or fast. His mechanics are pretty good. I can work long sessions with him and not hurt him.
Also, I can get a head start on curve balls and sliders without letting him throw them in a game or at a speed that will hurt him. He has a pretty good curve that is warehoused for later.
At the end of the sessions, we back up to 2/3 then full length and he throws a little full speed. At full speed, I quit talking mechanics and tell him to find his rhythm. This is a missing element in so many paid for lessons.