The entry-level Futaba radios have that little push button on them. The higher-end radios have a momentary bat-switch (toggle switch) that your left index finger hold in the up position to give the student control. For the instructor to regain control he just lets go of the switch.

It is a LOT more comfortable than the push-button. I guess they figure the entry-level 4 channel radios are more likely to be the trainee radio instead of the trainER radio.

By the way, congratulations on getting your son interested in RC flight! THAT is way cool.