OK I didnt come across this with my older two boys so am starting to run out of ideas...

Joshua is 12 he will be 13 in a couple of weeks and is driving us mad, he is tormenting the younger children being lazy not helping unless its with a nasty comment or face.

He has never been any trouble he was the ideal little lad happy go lucky always smiling. He still smiles all the time but is hurting the younger children by being too rough when he plays with them to the point that our five year old said 'when I am a teen I wont hurt anyone'. He is a bit cheeky to me as well although not his dad who is stricter than me I admit.

I have toughened up with him and he knows I will not back down on things I say now.

We have tried the following.

Turning things into fun.
banning him from playing with the younger children.
Told him his skiing trip wont happen if he does not stop (he knows we will do this).
Talking to him like an adult and trying to reason with him.

What else can we try ?