Stand along the wall in the shallow-end. Step on the noodle with your far foot and put it slightly in front of your body. Hold the rail (or the side of the pool) with one hand. Keep your arm straight and relax your shoulders. Put your other arm by your side.
Bend your leg up at about 90 degrees then extend it in front of your body, at about your hip level. Bend about 90 degrees again and extend your leg deep down, returning to the standing position. Try to keep your movement continuous when switching between the front and the deep extension (so try to perform it as a single move). Avoid doing full leg extension, but rather you should keep your leg slightly bent as you move forward and downward, and keep your hips still as you extend forward.
Inhale as you extend your leg forward. Exhale as you extend down.
Use your quadriceps to extend your leg in front and down. Use your hamstrings to pull your leg back.