The fun of the Fiftieth Day of School just keeps hanging on! Writing non-fiction is very different than writing fiction and having some experiences to 'hinge' our understanding onto makes the actual exercise much easier. Bubblegum was a relatively new chewing delight in the 1950's and being able to blow a bubble with gum is a sign that you are really growing up!
What are the items that are needed if you want to blow a bubble? What are the steps to creating a bubble? Could you write these down in full sentences in order and have a reader follow them?
When the students write their sentences, they have had the opportunity to try, to talk and share with others, have created a plan and have reminded to use the mechanics of writing appropriately. For all of that, you will notice that some still do not start sentences with an uppercase letter, end with punctuation or spell the words (or copy them) correctly. That makes the difference when assessment is being done.