Actually, their shyness, schooling behavior depends on the envirnment their in, the fish kept with, and how many cherry barbs you have.
I had 4 kept in a tank with a lot of active fish. They were shy.
I had 6 of them in a tank with a few danios, the male was actually very aggresive, as he was ready to breed.
I have kept 8 of them in a fully planted tank, and they paired off, kinda shy and hanging out.
Now I have 3 males and 2 females left, they are a few years old, and they don't really school, they just pair up, or three of them will swim half way across together. They are in a very active tank, and are not shy at all.
My males don't even bicker, so 3 and 3 would be the way I would do it. Right now it is 3 males and 2 females for me, and there is not a problem.
Great fish!!