It is widely accepted that the Back Squat is the "king" of all lifts.....or to be fair to the ladies we train, the "royalty" of all lifts. In other words, if you were only allowed to do one lift, the back squat would be it. In just the one movement, it provides major athletic benefits (speed, power, flexibility, balance, and of course strength). In just the one movement, it provides major health/wellness benefits because it develops the biggest concentration of muscles in your body, thus increasing lean muscle, thus increasing metabolism, thus increasing fat burn, thus making one "healthier".
(Before I go on, I know there are people who can justify why another lift is "king", (perhaps the Olympic lifts), but my opinion and purpose for this piece, relates to back squat. So if you disagree with me, no problem, but I'm not looking to start a debate on which one lift is the best.)
But as we know, especially if you work with kids, the back squat is hard to master. Teaching it forces us to use clear and concise coaching points like "chest up", "butt back", "feet flat", "sit tall", etc. Sometimes, the simple repetition over time of doing the back squat itself can help a kid learn the proper technique. We can use lighter bars, PVC pipes, benches, boxes, and physio balls to aid in the learning process. Supplemental lifts like lunges and box step ups are also good to develop the hip strength and flexibility needed to back squat well. I have used all of these methods in working with the high school kids I do.
Recently though, and this may illicit a big "duh", but I have been using the front squat and dumbbell squat as means of training for the back squat. I've learned in many cases that kids are better front squatters than back squatters and that dumbbell squats prevent the load on the low back and force the kids to only use a certain amount of weight because they can only hold so much in their hands. Along with teaching depth and hip flexibility, the front squat also prevents too much weight from being used because they just can't hold as much in the front of the body as compared to the back. I make the poundage point specifically, because I have several 15/16 year old boys that try to increase weight faster than their technique allows. It can be challenging to keep control of their weight increases, even if we work off percentages. These variations keep them safe while teaching good habits.
How long I use the squat variations before having kids back squat depends on the individual kid. Even after the back squat is introduced, we go back to the variations for the training effect of those lifts themselves but also as a way to reinforce the mechanics we want in the back squat.
Again, all of this may seem pretty obvious to most of us but, I've been a working S/C coach for 9 years and have just fully realized this. If it took me this long, then I'm sure there are others as well.
I hope this helps someone.