Good question--complicated. This gets into controversial socio-political territory real quick. I'll try to avoid that.
1. The institution of education is strong (the might seem counter-intuitive at first). Any student willing and able to learn in nearly any school in America has access to a great education.
a. Some students are not willing: factors include laziness (very rare), broke family structures (most common), and some systematic cultural bias from teachers (controversial territory). Everyone is guilty of cultural bias. My students are 98% Hispanic. I teach English and do not speak Spanish. We have some significant cultural differences. When I first began teaching, I realized my concept of what is and isn't respectful behavior was different from my students. They were not trying to disrespect me, they just had a different cultural operating system. They thought I needed to earn their respect; I though teachers were already deserving of respect until they lost it. I got angry a lot before I figured that out. There are many examples like that. Most teachers are white, like me. When a white teacher has little cultural connection to diverse student populations, they often struggle to become great teachers. This is one reason older teachers are needed. However, most teachers leave the classroom after five years. Young teachers = struggling students.
2. Parents. Research is clear; students who grow up with forty or more books in the home are far more likely to achieve higher standards and attend university. These students have a strong advantage--that's great. Parents who read to their kids past childhood (adolescents) have an extraordinary advantage; this is equal to a private school education. Most students do not encounter this advantage from the home. Teachers cannot effect parental changes of habit. We can only work with what we've got.
3. Poverty. The struggle is real. Many students are what we call food insecure; they may only eat at school. This is sad. Parents often cannot afford school supplies and school budgets often cannot supply them either (consider
Donor's Choose, as a tax exempt donation). This is me being political for a second--we need tax increases to better fund education--end political talk.
Actually the list of why the education system is failing--it isn't just the education system that is failing--Americans are failing our kids. We are all to blame--that's why I joined the fight. I got out of the military and now serve my country by being a teacher. Please help--the kids need all of us.
The students who have all these resources are doing great. It isn't a kids fault they were born with disadvantage. Sweden and Norway do well because they have less poverty. We need to help our students overcome poverty before we can expect them to thrive as scholars.
Sorry this is so long--trust me, it could be a lot longer. Please anyone--jump in with thoughts or a critique of what I said.