Teaching the fundamental squat can be a challenging task when considering the fact that everyone has their own perception of what the correct performance of a squat is. Wikipedia identifies a few of the variations of the squat but the most misunderstood (important to clearly define) concept is that the Back Squat specifically is one of the three lifts in the strength sport of power-lifting. More later on the evolution of health and fitness in our North American culture over the last 100 years later.
From a rehabilitation and movement perspective I am referring to the squat from a fundamental movement (neuro-developmental) perspective. As we grow and develop, specifically from birth to 12 months of age, we earn our movement patterns by learning and often failing in a rich sensory environment (great 3 DVD set from Gray Cook of Functional Movment Systems and Erwan Le Corre of MovNat on Exploring Functional Movement available that really expands on this). We learn how to squat at an early age and we learn from the ground up. That is we literally start on the ground and stand up from a deep (but on the ground) squat. In training and rehab many time we need to reverse engineer the squat pattern with a stepwise progression. One technique is to teach the dead-lift with the help of handrails, or a physioball in this example, and progressively lower into a squat posture and return to a standing position.
The take home message: Provide exercises that challenge your clients to successfully move on the edge of their ability and allow them to earn, or in the words of Gray Cook "own the movement"