First: U.S. schools are ideologically predisposed, for a variety of reasons, to defending and propagating a specific, very conservative, idea of history and the world. From what is taught to how it is taught, obedience to corporate overlords, acceptance of violence, and an idea of America as exceptionalist is deeply ingrained in the curriculum.
Second: U.S. schools have serious problems with gender bias. Both girls and boys are affected by these problems, though the fears about how boys are treated is often exaggerated with hysterics.
Third: U.S. schools are unequally funded. Because of the reliance on property tax and because of other funding priorities and mechanisms, American schools are effectively both racially segregated and economically unequal. This leads to unequal outcomes.
Fourth: U.S. schools fetishize standardized tests. Metrics can be good, but the problem we have is two-fold: First of all, we punish failing schools instead of giving them more resources to allow them to succeed; second, we use metrics that are flawed on their face, racially and culturally biased, and spend so much time getting metrics that we actually prevent a quality of education. When there is a good test that examines if someone has learned critical thinking, emotional intelligence, life skills, and how to be a good citizen from school, then those tests will be worth it. Until then, they are overwhelmingly distractions.
Fifth: U.S. schools too often propagate racial bias. From the way that tracking is conducted in an often-racist way to subconscious and conscious biases on the part of teachers to the least qualified teachers being assigned to the students who are struggling the most (when it should in fact be the opposite), U.S. schools perpetuate racial inequality far more than they prevent it. Worse, they tend to then push students into other associated biased institutions: Schools rarely help students deal with any kind of stereotype threat, which causes inequalities in test scores.
Sixth: On average, teachers are paid too little and there are either too many students and/or not enough time for teachers to be able to prepare lessons and deliver quality education.
Seventh: Curricula are flawed on multiple levels.
The solution is not to prioritize charter schools or private schools. Those are fine institutions and should receive appropriate support, but the public educational system must be competitive and produce critically-thinking empowered adults.