Matter was a unit in the science curriculum that I taught. Teaching about solids, liquids, and gases involves lots of experiments and hands on learning. Every year as a culminating activity for the unit, we would make ice cream in a bag. It’s fairly inexpensive, uses items you can find at the local grocery store and teaches the students first hand about the change from solid to liquid. Plus, they have lots of fun and get a tasty treat at the end!!