I have found that with my 6 yr.old he knows what he needs. Just this morning in fact, he had a meltdown and would not cooperate with doing his schoolwork (homeschool).
My first instinct was to stick him in a room to calm down. Didn't work. Seemed to make things worse. My son is a sensory seeker and when he came out of the room, he told me he needed to be shut in the large dog crate before he could be happy.
As bizarre as this may seem, I complied. My son then promptly began scooting the crate across the room over the hardwood floor and down the hallway. It took a great deal of effort on his part of back and forth movement, shoving the crate (from the inside) across the floor.
After ten minutes of this routine, he let himself out and was his usual cheerful and compliant self.
This isn't the first time he has found something on his own to expel his pent up energy and anger. I just have to remember to step back, observe and assist if needed as he figures out on his own how best to meet his needs.