In terms of public high school, I think grading is the biggest problem. The old saying is that a "C" is average. If that was true, most state colleges would have an average acceptance GPA of like 2.5. Schools hand out A's nowadays in an effort to just get kids through, because they would feel too bad breaking it to them that they shouldn't go to college.
College used to be something very prestigious. The best performers went, and those that didn't worked for them. Now it's like an expected chain, even those at the bottom of the totem pole get a degree.
Yeah, only problem is a C at a public college prep school and a C from the school in the ghetto are not one and the same.
Another problem with education at lower levels is the fact that many teachers (but not all) are not at the top of the ladder when in comes to how well they did in college. (I know its faux paux to say its not all about the money when it comes to choosing an occupation, but when you have several options it really is. If teachers were paid more, that definitely would've been a option). Which leads me to believe, that teachers do not get paid as well, or receive the respect that they deserve, Most of us here wouldn't be here if it wasn't for the teachers we had.
As ramble as that was, here's is some more rambling, Another problem with education, many people view it as a hassle, and not a road to success.
Some parent's don't take enough initiative to help/guide their child, and blame it all on the teacher when the child does poorly.
Not enough emphasis on math and science.
Putting kids with different levels of skill in the same class. (I think the high school/middle school model with different teachers for different subjects should extend down to the k-6 level.)
Standardized Exams, yes I understand that they are supposed to level the playing field, but this leads to two problem, teaching toward the exam, and for those who are way above average, they have to take a step back to relearn 'the tricks' of what they may have covered years before. (i.e. taking the SAT's when you are already in Calc AB.)
And as hoity-toity as this may sound, I wish that there were programs (for say high schooler), from lower performing schools visit higher performing schools in the same area to show them how far behind they can be/are.
I could go on and on, but that's all I have for time now.