You usually don't practice gliding when learning how to fly a small aircraft, they simply don't glide very well.
What you of course do are power-off landings – on airfields, for example from the downwind, and simulated, i.e., you make a go-around just before landing, outside an airfield. Sometimes, it works, sometimes, it doesn't, there are many factors … that's why you actually fly with power idle and not with power off. There're still a few incidents, i.e., somehow the practice becomes tool real!
All in all, power-off landings and other emergency training are an important part of becoming a pilot but you don't spend that much time for them. Other things are much more time-consuming in a typical 45-hour syllabus.
Related fact: the glide ratio does not depend on the aircraft weight, only on the aerodynamic efficiency (the ratio between your lift and your drag), so it is useless to throw weight to reach further like maybe you have seen sometimes on movies. Less weight will make you descend slower but not further. Normally, the longer your wing, the higher your efficiency. See for example the pictures here: https://en.wikipedia.org/wiki/Aspect_ratio_(aeronautics)
Losing weight will reduce stall speed, allowing for a slower and safer landing. Modern competitive gliders carry a substantial quantity of water ballast - the extra weight improves glide speeds, but it can be jettisoned before landing.
I doubt they practice it much in 767s, though, despite the fact that they actually glide better. :)