This is an excerpt from Assessments and Activities for Teaching Swimming by Monica Lepore,Luis Columna & Lauren Friedlander Litzner.
Skill 2.4 - Bob Five Consecutive Times in Chest-Deep Water Independently
The student and the instructor are in chest-deep water next to each other.
Hold a pool noodle 6 inches (15 cm) over the student's head. Tell her to bob five times and try to have her head hit the noodle as she pops up out of the water (make sure to explain that the farther down she goes, the higher she will be able to jump).
On your signal, the student bobs five times and tries to have her head hit the noodle as she pops up out of the water.
In the activity Head Start, the instructor lifts the pool noodle higher after each successful attempt.
Learn more about Assessments and Activities for Teaching Swimming.