The FOSS lessons for our unit of study on rocks include experimentation of river rocks. On Day 1, the students sorted and explored river rocks. The sorting was more challenging that simple colored blocks but many students still were able to sort. The students recorded their observations on educreations.com (all ipads were signed up to my account so I have access to each of their recordings).
Here is another student's sort.
I am also able to instantly share their labels using the apple tv. Each child's ipad is on my network (the one named after me located in my classroom). I just project the child's ipad image on the screen (the same way I do mine).