Teach the basics of writing a sentence at all grade levels. Often students have creative ideas for fictional and non fictional material but their sentence structures are weak. Strong sentence structures are imperative for the students to create excellent reports and stories.
Write on chart paper the basics of a sentence and display it in the classroom in a highly visible area. As well, weekly or monthly have students dissect sentences for their weaknesses and strengths. An example, is write a very basic sentence on the board and students are to add detail to the sentence to make it more interesting. As well, you may wish to write poorly structured sentences that students need to correct.
Often students have wonderful ideas but find it difficult to transpose their thought into a sentence. Continue to reinforce the basics and you will find students writing awesome sentences in no time.