Nowadays, it is standard practice to use a buddy box system during preliminary flight training, this being the equivalent of dual controls in a full size aircraft. Typically – two transmitters are connected by a cable, although this is now being replaced by wireless systems. The instructor has a switch which enables activation (or not!) of the control sticks on the student’s transmitter.
These wonderful set of photos of the Buddy Box system in action are courtesy of Cec Marshall, Mark Primavera, and Peter Smith.