I love this! I was a lifeguard during college too, and I wish I'd thought of that. I used to keep cards with the numbers 1 through 10 under my chair and when I was assigned the diving pool I would rate the kids' dives.
Here's a funny lifeguarding story (funny only because it turned out okay.) A small girl, maybe 5 years old, was on the diving board. Her parents were watching, so we all assumed the kid knew how to swim. She jumped in and immediately started to struggle. Mom jumped in right after her, which turned out to be a terrible idea because Mom immediately started panicking too. Then Dad jumped in after both of them and promptly started drowning as well. There were the three of them and four lifeguards in the water before it all got sorted out. The lesson? Please don't let your children dive when they can't swim. And please don't try to save them when YOU can't swim. Thanks.