We've all seen those run on sentences that never seem to end. It's great when a student has lots to say and can include many details in their writing, but sometimes they forget about structure. It is important to teach them how to use proper punctuation and capital letters in their writing. Editing sentences daily is a good place to start. The more often students are writing, the more likely it is that they will remember to use proper form.
It is good to start teaching this skill by showing what a complete sentence looks like. It starts with a capital letter and ends with a punctuation mark. Coming up with a list of when to use capital letters is a good idea. Be sure to hang the list somewhere in the room so students can refer to it when needed.
Next the students correct sentences that are missing the capitals and periods. This helps them to clearly see the beginning and ending of each sentence.
When they have had enough practice correcting sentences, they can start correcting short paragraphs. They will develop the skill of seeing where one sentence ends and the next begins.
In addition to daily worksheets, students should also evaluate their own writing to see if they are using capitals and punctuation correctly. After the first draft of a writing piece, students go back and revise and edit their work. This is where they might discover that they have missed some much needed punctuation.
The activities shown above are included in my Sentence Editing resource.