This activity is designed to be completed at the local pool, possibly during a prac double & preferably early in the semester. This way you can develop an initial impression of a) student competence & confidence in & around water, & b) student cooperativeness during excursions. You will also have a record of swimming & self-rescue ability.
Students, of course, will need to be monitored closely, & in most cases, take turns to practise & perform tasks.
Skills can be assessed as a part of a “routine.” For example, students can enter the water with a slide entry, swim 50m wearing outer clothing, remove outer clothing in deep water, continue swimming, etc.
Most of these skills are taught as a part of general bronze courses, & are described in various manuals.
Some of the tasks inevitably have a competitive element that provides extrinsic motivation.
You would expect the boys to be less buoyant than the girls (buoyancy being one of a series of physiological advantages that females have over males!).