Great lab and wonderul use of the UDL principles. You were able to create a hand-on lab experience while integrating technology! I like the idea of giving the children a real world problem and allowing them to investigate it using another material (i.e. seeing the effects on plants by studying the onion). I might suggest that you pair the stronger students with the struggling students as opposed to allowing them to choose their own groups, this is a lab that could benefit from teacher guided pairing.