What are some fun, engaging hands-on activities or demonstrations about the three states of matter for a third grade class?
—B., Tennessee

I think that the best activities with the states of matter involve the changes between states. You may want to review a recent post in which I shared several ideas for activities related to gases. (http://bit.ly/2MnnbnR)

Ideas for liquid/solid activities:

Ice cream in a zip-top bag
Ice cream is more than a sweet treat—it also can be a lesson on depressing the freezing point of water using salt. Record the temperature of the water during the activity. Always double-bag the liquids to avoid salty ice cream! Make sure to provide alternatives to accommodate any dietary restrictions.

Gelatin or chocolate molds
Candy molds take advantage of major properties of liquids and solids: Liquids flow and take on the shape of their container; solids maintain their shapes. Use a gummy formulation for the gelatin. Be careful with hot liquids.

Resin casting jewelry
Purchase two-part resin or epoxy to make jewelry in molds. (Don’t reuse the same molds for edible treats). Prepare the molds with a release agent like vegetable oil. There are resins which are free of harmful out-gassing. Make sure to practice beforehand and always use gloves.

Non-Newtonian fluids
Students will be astounded when they play with these bizarre starch solutions which behave both as solids and liquids. Easy, safe, but messy! Be sure to cover surfaces and wear smocks.

Hope this helps!

Image credit: CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=48897