First of all, congratulations to your son for getting into dance.  Although it isn't the most popular activity for teenage boys, it has many rewards for those who take the plunge.  Although you didn't mention which branch of dance he is starting, can we assume it is ballet since he's wearing tights?

Unfortunately, as he's already found out, dance can be downright painful if you don't wear the right things.  Tights don't offer any significant support to the male genitals.  In addition to the obvious problems of bouncing and clanging around during jumps, his testicles could get trapped between his legs during simple moves into sous-sous or 5th position.  Micro-traumas to the plumbing can create longterm problems as well as immediate pain.  If you ever expect to have grandchildren, get him a dancebelt immediately and make sure he wears it!

Dancebelts are a sort of specialized jockstrap designed to be worn with the male parts pulled "up".  Most have a three inch wide waistband, a semi-flat front pouch, and a thong rear.  The thong not only helps keep the dancebelt from showing strap lines under tights, but means there is no pressure across the gluteus maximus (butt) muscles, so it doesn't slip or create pressure there while dancing.  Still, the thong is a bit unusual feeling at first and may take your son awhile to become accustomed to.

Dancebelts also streamline the male physique under tights, holding everything fully immobile so he won't need to make any comfort adjustments during class and insuring he won't be embarrassed by a spontaneous erection.

The most common brands of dancebelts are Capezio and MStevens.  Either will do the job.  A tan (flesh color) dancebelt is the best color since it can be used under any color tights.  Black can also be worn with black tights, but avoid white which shows through more than the other colors, even under white tights!

If you have any more questions, just ask the doctor.  I'm always available to answer questions about male dancewear.