Well, judging by my school days and where I'm at now in college I'd say several things. Number one, if you don't get on well with a teacher and vice versa, they could mess up your entire school life through bad student reports, such as misjudging your academic level, causing you to be in lower class sets (like what happened to me). Secondly, school systems are to heavily based around exams, even in primary school, which is stupid because when your in primary school, you don't care about doing well in school yet, because we're not mature yet, or have the drive to achieve well academically either and SATS results are taken too seriously, if you do poorly, you're screwed. Thirdly and no offence to them but a lot of the teacher I had in school were foreign and didn't even speak coherent English, which leads to poor education. Lastly, there is a serious lack in funding to state run schools and it's been that way for some time, I remember in science classes having crusty old science books, full of profanity and racial slurs.
That's what I think anyway. Oh and teachers are lazy, vindictive and not passionate about the job they do. They are always complaining about salaries and workload, which in modern times, compared to other jobs, really isn't as bad as they make out.