How would you deal to a child who can not write a single sentence and study in 6 grade?

While this observation is valid, and the problem is already there and cannot be denied, the child is only one element among many others leading to this result. 

I have a complete edicational (teaching/learning) model that can go in details in diagnosting these problems through "cause-effect" analysis, leading (hopefully) to remedial actions from all involved parties