The primary problem with the education system is that many kids have a horrible home life due to any number of causes including, but not limited to, generally bad parenting, violence, poverty, drugs, or abuse.
People think education happens in a vacuum where everything that doesn't happen at school doesn't affect school.
If they do acknowledge that a child's home life may affect their education, they expect the school to fix it all in 7 hours a day for 180 days a year.
Other things that negatively affect education:
Poor teacher pay to attract and retain quality teachers
Lack of resources to promote adequate learning environments (buildings and supplies)
The lack of emphasis on the value of education and hard work in our society (precious snowflake movement)
Excessive testing
The competitive environment being fostered by conservatives