I have no irons in this fire, but imho, i think that some of this could have been avoided had a couple of experienced divers been bringing up the rear. To play look out for the laggers and the ones that may have fallen behind for some reason.
I can only visualize how 19 students would look UW. I am sure disorganized would be one word that comes to mind. No matter whoes at fault, if there is any fault to lay, these were just teenage kids. We can harp all day long about gas mang. dropping weights and everything else, but these two were under age and still considered kids and preperations should have been made as such. More adult supervision, paring the kids with experienced adults, adding more adult divers on the dive, what have you. I would like to know how many adults were actually on the dive with the kids. I often wonder when something like this happens and it is reported, "when we surfaced they were missing from the group." I envision them being the last in the long line with nobody looking back to make sure all are still there. Kids have to be supervised at all school dances, proms, outings, what makes this any different? There should have been more adult experienced divers in the water with the 19 kids.
I have considered sending my daughter on scuba type trips and this is one reason that I always change my mind. If I could not be there and diving along with them than she should not be going. Granted my kid is much younger, but hearing stories like this are one of my worst nightmares.