Maybe you should take some additional classes with another teacher. Actually you can do some dictations, it is good for grammar and punctuation, and also improve some writing skills. Also, I can advise to choose the writing service (e.g. Papersowl) which will meet all your requirements according to its review. To do this you can surf detailed information on papersowl.com review and find the best one for you, write some texts as the examples and then on the base of them try to write your own. But often, the matter is in the approach of the tutor to the child.