Help your children to think more deeply about the story by asking open-ended questions such as “What happens next?” and “Why did he do that?” The more questions you ask, the more they think about their story and characters and the more they will find to write down. Before long they will learn to ask those questions for themselves and you will see their writing growing in scope.
Don’t just pay attention to a single written piece. Read all of the child’s work and look for similarities between them. That will give you clues about both strengths and weaknesses and help you know what needs to be worked on. For instance, one girl might have an active imagination, but none of her stories has a logical ending. Or if another boy writes about nothing but robots shooting at each other, then you know he needs to expand his subject.
Instead of asking children critical questions like “Why did you write that?” or “Is this your best work?” ask questions that help them improve. Say, “What did you learn from writing this?” and “What will you add to this?” Encourage them to recognize their strengths so that, instead of being discouraged, they will be encouraged to keep writing and keep improving.
If you work with more than one child, have them read their stories aloud to each other. Reading aloud helps them to evaluate their own work better, and children may be more receptive to comments from other children than from adults. If they learn to critically assess another’s story, they will be able to bring that skill to their own writings too.
Assessing creative writing is difficult because so much of it is subjective, and every person’s vision and imagination is different. There are certain things you can grade for, though, such as how well the story is organized, the use of description and proper spelling and punctuation. Whether or not the child has a natural flair for writing does not affect his ability to incorporate those elements.