It can be rather discouraging when a child simply dislikes writing. There could be one of many factors at work here. Let's explore some of the reasons a child may dislike writing and some solutions to address each of these factors.
The first factor is that perhaps your child doesn't like the physical mechanics of writing. Does he hold his pencil with an uncomfortable grip? Does he grip his pencil too hard and push too hard on the paper? Does he have improper letter formation that requires a lot more writing to form each letter? These things usually correct themselves, but not always. The best way to develop a love for writing is to require typing as a subject. My favorite typing programs are Mavis Beacon JUNIOR and Typing Instructor. My children were required to do their typing program every single day for a few months, and then only once in a while after that. They got even more practice after this as they wrote stories on the computer.
Some children don't dislike writing as much as they dislike having to pull creative thoughts out of their brains. I like what classical educators have to say about this: children need ideas put in their minds before they should be required to create new ideas. They should be filled with knowledge, ideas, concepts, truths, stories, literature, facts and information. Then, they should be asked to write about what they know, not come up with new ideas or required to develop an opinion. When they are older and have been exposed to great literature and a wealth of ideas, they will have a stronger knowledge base from which to pull creative ideas and thoughts. They will also have the critical thinking skills, the ability to conceptualize abstract thoughts. At that point, they can create a great composition, story, persuasive essay or whatever it is the writing assignment requires.
Another reason your child might dislike writing is because you, being the very thorough and wonderful teacher that you are, used their writing assignments as the examples of what they needed to work on in spelling and grammar. Every writing assignment became a poster of their weaknesses and failings. I have heard many homeschool moms say that they use their child's writing assignments to pick out spelling words, and teach proper grammar. This may be an economical use of their writing, but it is also a good way to discourage their love for writing. I often take my children's notebooks to conventions to show others. I had one mom tell me how pleased she was to see all the misspelled words in my daughter's notebook pages. My daughter was nine when she wrote those pages. She is now twelve and has developed a love and passion for writing -- and now spells better than I do! I never used her writing for spelling practice. She learned to spell using a spelling program.
Perhaps the most common reason a child doesn't like writing is because God did not design him to be a creative writer. This child prefers to solve problems (especially math problems). This child doesn't see the benefit of writing. It seems purposeless. Frankly, creative writing - writing to entertain - isn't necessary for every child. The only writing that is absolutely necessary for every child is academic writing. If the problems are not one of the above-mentioned issues, I would not force a child that has not been given a bent towards writing to do a lot of creative writing assignments. For younger students that dislike writing, I would require them to narrate constantly. Have them retell back in their own words whatever they read or have had read to them. This will go a long way towards good narrative writing. A child who can relate information clearly will find it easy to put those spoken words on paper. As he grows older, have him do just that. Put his short (or long) narratives on paper. In late middle school or high school require him to learn academic writing.
Creative writing is simply not for everyone. A child who dislikes writing can still make A's on writing assignments if he is taught how to organize his thoughts, and write a well thought out and organized sentence, paragraph and essay. This begins and ends with oral narrations, for even if your child becomes a mathematician, he will be required to explain his knowledge orally. Thus, in the early years, don't worry so much about writing - focus on his oration of thoughts.
If we had time, I would tell you the story of my husband - who didn't care for writing growing up, but learned to write a good essay and now makes a living by writing perfectly constructed legal briefs and other legal documents. But since we don't have time, just know - your nonwriter isn't failing at writing - he's simply expressing his unique God-given talents, preferences, gifts and abilities, which will all work together to usher him or her into God's special plan and purpose prepared in advance.