In our study of snow, we learned that snowflakes are formed from snow crystals. As the crystals fall from the sky, they clump together to form snowflakes. The kids and I did an experiment to see how crystals form. First, I had the kids make "snowflakes" from white pipe cleaners.
Any shape will do, really.
Next, we floated our snowflakes in a solution of Borax and boiling water by attaching them to a ruler laid over a large Tupperware bowl. For every 2 cups of boiling water, dissolve 1/4 cup of Borax. Add more Borax until a slight amount has not dissolved in the water.
Allow your snowflakes to grow crystals overnight or longer.
It took our solution about 24 hours to start hardening into some really sparkly crystals. 
