One of the most useful items an Instructor can take on a flight is
a spare chart and masking tape.
the moment you a student starts to fixate on the panel and sacrifice a lookout, you tape over the entire panel and develop their scanning outside the cockpit.
In a Decathalon from the rear seat you have NO instruments what so ever, and you have to get the student to clearly understand that They have the better visibility and they have to keep the lookout, and if they dont they might kill both of you.
I show that despite not being able to see any instruments at all, that I can rattle of the airspeed within 5kts, the amount of G being pulled, or was pulled, and once told an altitude, I can guess when the circuit altitude has changed into a climb or descent that might breach goals or limits.
Glass Cockpits do breed a false sense of infallibility, and total reliance that can and will kill.
While we have Flight Schools that have incestuous hiring of the instructors that they train by instructors that they trained, the value of that training will slowly eradicate practical standards and the most simple of all tasks of insuring that eyes keep outside the cockpit.
Even Head Up Displays have a danger in that the eye focus is at the windshield and not at infinity which means distance vision is lost.