My initial approach would be to have a discussion with you about the issues facing your child. Ideally, I would then look through some of their recent work to discover their strengths and weakness. They might have issues moving from simple to compound sentences, or from compound to complex sentences.
Other issues might include spelling, punctuation or general grammar. They might need to focus on using more connectives, or adverbs, or working on their descriptive skills.
I would look at the requirements of their particular National Curriculum level and design work, which we would do together, to support them. I might also look at end-of-term or end-of-year tests (for instance in shorter or longer writing) and then model an approach to answering the question. We might do the plan together and then discuss how to transfer this to a written paragraph.
If there is a particular topic or issue which your child is covering at school, I could offer support in our 45-minute sessions. Hopefully, this would transfer to greater confidence and achievement in the classroom.
My aim would be to support the work of the class teacher and to complement whatever was going on in the classroom. I hope this would help!