(whew, that was a lot :)
1) Tens Rods and Ones Cubes measure about 1 cm in width; so I just take a ruler and mark small nicks 1 cm apart on the sponge
2) Then cut and that's it.
It doesn't come out perfect, but the kids still understand that 10 ones cubes equal 1 ten rod. It gives them a 3D tool that is cheap, cheap, cheap!
Have fun! If you would like more DIY Projects, check out my pinterest board: DIY Teacher