Scratch piano with play-dough and a MakeyMakey. My 4th grade student helper suggested we make a CSW account for Scratch so that anyone at the workshop can use the common account to create content. She made this for me... she even took and uploaded the picture so the background would be realistic. I think it's pretty awesome.
Here is the LINK to sign your student up to participate in the John Muir Science Workshop on Wednesdays from 1:30 - 3:00.