In a flap
Sometimes I have to admit to being flappergasted.
Consider what the purpose of flaps are for.
1) to provide the pilot with good forward vision during slow flight (such as the approach).
2) to allow a higher power to be maintained; piston engine temperature, torque with a turbine. if a piston, reduced likely hood of plugs oiling and caburettor icing.
3) the benefits of propellor slipstream effect
4) Reduction in the stall speed
Flaps should not be used to get out of trouble such as when high and fast - power and attitude does that better. Raising flaps could lead to a high rate of sink just at the wrong time.
The pilot should know the reduction in airspeed that each stage of flap will generate and plan for that accordingly. Dragging the aeroplane in all the way from base leg seems futile to me.
With regard to the C172. If on the initial approach (base leg) the aircraft is configured with 10 degrees of flap and trimmed 80kts IAS then following with flap 20degrees will achieve 70-75kts, 30degrees 65-70kts and finally 40degrees if you have it will result in 55-60kts. Knowing that you then must decide what you want given the conditions. The student must understand that the greater the deflection of flap the less will power exceed drag during the approach and also during a go-around.
The PA28 first trimmed at 80kts with flap 10 degrees will thereafter give at flap 25 degrees 70-75kts IAS and with 40 degrees 60-65kts.
Whatever the aircraft the student should know the figures for their aeroplane and use them accordingly with purpose. The student then can be taught to use them intelligently to suit the prevailing conditions.
The scrapyards are full of bits of aeroplanes because the pilot tried to arrest speed and lose height on approach without a thought to reduce power. Unable to arrest descent in windshear or perhaps unable to make a succesful go around.