Do we have to pull a boy foreskin back to toss him off?

It would definitely help. as the foreskin covers the glans which are the most sensitive and erogenous zone on a male. The action of the also very sensitive foreskin rubbing back and forth over the gland makes the whole experience very pleasurable. I doubt if it would work without it being able to move backwards and forwards, If it is still tight over the head of the penis it is just a mater of stretching exercises which can be achieved by literally grabbing the foreskin and puling at it and stretching it gently in as many directions as you things will loosen it. Do this a couple of times a day, or more if you like and it will be working properly within a coupl of weeks. Be gentle with it .