It's the practice in my son's studio for the boys to use homemade elastic belts to keep their tights up. You take a 1 inch wide length of elastic and sew on a snap-together fitting and the loose end can be cinched up.
DS pulls his tights as high as he can get them, then slips on the belt and tightens it. Then he slides the belt up and starts rolling the tights and belt over and over until it hits his hip.
Sometimes he'll forget, or misplace, the homemade belt and he'll just use whatever belt he can find - leather, webbing, etc.
Is there a better way? Any tricks of the trade he may benefit from? Nothing worse than a saggy crotch in his tights!
BTW he's very slim. Maybe it's not an issue for more muscular boys?