Knowing the student’s dominant side is important, because you want to start each piano-exercise by using their strongest side, because it will make them feel more confident, and they will be more successful.

Knowing the Right Side from the Left Side is a learned concept, not a natural instinct.

Never assume that someone naturally knows their right side from their left side. Learning left from right is a confusing concept which requires repetition and patience.

You can start introducing Right and Left by using the student’s dominant side. To find out which side is dominant, ask the student to cross their legs and watch which leg they place on top.

You can also ask them to listen to a sea-shell and watch which ear they raise it up to.

Those are fairly reliable indicators.