Second graders had an in-depth discussion about what would possibly have given such differing results. Here's what they came up with:
1. We all didn't start with the same amount of water in our graduated cylinders. We probably should have.
2. Some groups "double dipped" with their material, causing it to absorb more water than it actually could.
3. Some groups squeezed out the water back into the testing cup, releasing water that it really absorbed.
We all agreed to do the experiment again, so that we can hopefully control all those variables and get more reliable data to inform our engineering solution (to design a baby's bib). Keep up the great work second grade!