I went to a government high school in the 90's in South Africa. Experienced teachers were given early retirement and replaced by younger teachers who, through a combination of ineptitude and inexperience, struggled to teach.
My grade 10 and 11 maths teacher couldn't factorise polynomials consistently. She'd often get stuck while halfway through a problem while working on the blackboard. Euclidian geometry was a challenge, and she failed to communicate theorem proving techniques. My Grade 12 (final year) maths teacher was promoted out after 3 months, and replaced by someone who didn't appear in class regularly.
I went for additional after-school maths tution, and I did very well during the exams in the topics that were covered there, but unfortunately we couldn't redo the whole syllabus. So my Higher Grade C for maths, although better than the majority of students in my school (and the country I guess, which has very low, and still-dropping educational standards) was disappointing.
We also had serious problems with our science teacher - retired, and replaced with someone who also never really used to pitch up. My parents bought me physics videos from the Learning Channel, a video-based system, and I managed to get an A. Unfortunately their budget didn't stretch far enough to buy the maths videos as well.
I have watched Khan's videos and I always wish that that sort of service was around back when I was in school. Yes, I, and most of my friends may have been deprived of some conceptual understanding, but at least we would have gotten some teaching. Something is better than nothing, at least for those of us who don't live in US College towns.