Typically, it will need around 3 flights to ensure the candidate has the skill to glide the aircraft from around 2500 ft to a survivable landing in a field
A bit of history from the early 1950 era when I learned to fly on Tiger Moths where every approach to land was by a glide - not a powered approach. If power was needed to salvage a under-shooting approach to land, you lost Brownie Points and needed further dual until such times you could consistently land safely off a full glide approach from the time you closed the throttle on mid-base leg.
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Same technique of glide approaches applied to Austers, Chipmunks and Cessna light singles. Turn base in level flight, maintain height on base, and when you judged you could safely glide in you simply closed the throttle and used airmanship. If you were forced to fly further downwind in the circuit because of an idiot flying a 747 circuit, you maintained circuit height as usual on base and if necessary early final still in level flight, then closed the throttle when you felt you had it made and did a glide. Of course with heavier types powered approaches made sense. A full flap glide approach in the Australian Wirraway (similar to a Harvard) was quite alarming with its very nose down steep approach to keep the speed up and gradual early round-out because of inertia. Powered approaches were the norm in those types
For the light trainers, when the time came for practice forced landings in the training area you were already reasonably competent at glide approaches.
Somewhere along the years all that changed when the first Cessna and Piper singles equipped with flaps came into the aeroclubs. Now glide approaches were only introduced for practice forced landings in the circuit. Engine assisted landing approaches became the norm, despite it was unnecessary. The Cessna manuals said landings could be done with or without power. So you didn't need powered approaches except under certain circumstances. So today we have the complicated version of turning base clean, throttle set to 1500RPM - lower a little flap at a certain airspeed. Progressively lower a bit more flap at a new airspeed (flap against power..) and the resulting combination was different speeds for variable flap settings settings; all the while maintaining 12-1500 RPM for a powered approach.
No wonder students had trouble remembering all the combinations of RPM, airspeeds and flap settings.
Why do you think the time to first solo has blown out to 15-20 hours as against the average of 8-10 hours in the early days of Tiger Moths which had no flaps, no radios and required a keener judgement of the glide path