I like to teach that it is desirable not to get further than gliding distance from the airfield when flying curcuits. At least if they suffer an engine failure they have a chance at a safe landing rather than ending up in a factory roof, even if it's not on the runway.
Generally with glide approaches I try to do them when we are number one in the circuit. I pull the power on late downwind (at 1000 ft) and get them to use their track (ie, cut in or extend) and flap make it in safely. Most manage quite well once they realise they need to start a turn towards the rwy straight away. I get them to aim for a point about 1/3 of the way down the rwy. That way, if its all going well, bringing on flaps will bring their touchdown point back towards the threshold. If not, they can delay the flaps and still have a chance of getting it onto the rwy.