One of the most critical things for a student pilot to learn is the radical difference in glide slope control between power on and power off. In fact, with power on, glide is primarily controlled using various power settings within a functional range of angle of attack. However, without any power, glide slope is primarily a function of airspeed, and airspeed is a function of angle of attack. It's for this reason that glider pilots have a head start when they take up power. They have a good part of the emergency procedures wired, and more importantly, they don't panic when they lose power. At any rate, here's the most impressive demonstration of "power off" glide slope control you're ever going to see. I got this via Radley Balko.