not so much the working hard, its the lack of standards.
Student A, parent cares, kid cares, makes kids take harder more advanced classes, higher algebras, physics.
Student B, barely shows up takes dufus classes, bare bones minimum math, can barely read, has no idea how to write a basic paragraph. Can't find France on a map.
Yet both walk out the door with the exact same diploma in their hand. THAT is the problem. You will always have those that can't or wont learn, handing them a diploma, makes it meaningless.
I would think in most cases public schools can be ok as long as parents are involved in the classes and schedule Johnny takes and dontlet him pick them.