the school agreement and getting a child to play ball

[bronze]

Ds2 is due to start school in september. He pottytrained fine at 2 1/2 but never at nights but in the last year or so has started pooing himself bcause he can't be bothered to go to the toilet.
In the school agreement it says that the toilet has to be able to toilet themselves which is fair enough but I can't force him to go in the right place. Sitting him on the loo everynow and then makes no difference.
What do I do?

I would have thought the amount he goes it's all of it not just leakage if that makes sense. I'll see how it goes when hes 'trying' to make the effort of getting to the loo this weekend and if not I'll take him to the gp