When do squats start becoming effecive?

Are you working to failure? You could consider upping the weight and lowering the number of reps (3 sets of 6-10 reps for example). Even doing this one or two day a week could help. It's not neccessarily about volume but intensity is important

^^^^ this

I front squat fine. The bar situates above center of gravity which is what is most important in squatting. Front squats generally force heavier glute contractions, though lowbar induces much heavier overall recruitment of muscle in the lower back. The hardest thing for front squatting is to get elbows in the right place. To teach the squat, back squat is a much more appropriate place to start. And we have to admit that it is paramount to kinetic chain conditioning.

many years ago (late 70s) when kettlebells had their first boom, we had a coach that used them while facing(very close) a wall to teach good form for the squat now that i am older they seem to do the job on their own

Thanks for the advice :-) I do feel it after 3 sets of 20, just not as much as my shoulders do! I think I'm just not lifting heavy enough with the squats, as I do feel it with my dead lifts. The 141 kgs does feel like hard work, I was puffing and sweating like crazy, but it just doesn't hurt..although now from what I've read, pain isn't always an indicator of a good workout.

I also do want to keep trying with the barbell squats, but the trainer who is generally around at the time is an *kitten*. I might seek out another friendly face and get them to help me balance and check out my form. Perseverance!

This clarifies things a bit. You're holding a plate, that's basically a front squat. Generally speaking, your upper body will give out before your lower body when you're front squatting (they're still a great exercise though).

Maybe try these? http://www.exrx.net/WeightExercises/Quadriceps/BBHackSquat.html

When working your back squat, you don't NEED a trainer. It helps, but if you don't like the person don't. Take your phone or something and take a video of yourself doing the movement, then either post it online for review or compare it with other squat videos. Obviously stay VERY light while you're doing this.

Another suggestion I'll make is increasing the number of sets you do and working to make each set more explosive. Lets say you're leg pressing 3 sets of 20 right now and each set takes about a minute and a half to complete (~4.5 seconds per rep). If you're not feeling sore after (there's a difference betwen soreness and pain mind you, sore is just a feeling like you really worked hard, you can feel the muscles you hit, and you don't think you could do much more of that type of lift; pain is pain), try 6 sets of 20, or 10 sets of 12. Also try to shorten the amount of time it takes to complete your sets, instead of averaging 4.5 seconds a rep, try to average 3.5 seconds a rep. You don't do this by speeding through the negative, but by exploding through the concentric portion of the lift (the press part). If you start running out of time for your workout because of the added sets, limit your rest time between sets to 30 seconds to a minute.

I don't know if anyone suggested this at all, but something that could help is not using runners for your barbell squats. Best is barefoot, but i wouldn't do that at the gym. So anything that has a flat sole or those vibram fivefingers. The curves in your shoes can make a huge difference when it comes to balance while squatting or lifting in general.