Writing is a major cornerstone of the learning that we complete in school. The standard of writing expected of primary school age children is way over and above any expectations that would have been required in the past.
Children are expected to write at length in neat, joined handwriting. They are also required to use correct spelling and grammar and understand technical terms such as modal verbs, passive and active voice, word classes (used correctly), fronted adverbials, main and subordinate clauses as well as a range of other complicated techniques, which can be found here:
It is much more complicated than simply writing stories, to achieve well, your child will need to use the techniques mentioned above across a wide range of different types of writing.
The best thing that you can do to develop the writing skills of your child is to get them to write as much as possible at home.