To be a good student one has to be willing to learn. There are people in life who choose not to learn. There are also students who have little motivation to learn. And then there are students who are unable to learn in a typical learning environment. These are just three examples of what someone may label as a "bad student".
There are also teachers who have little motivation to teach. Teachers who are not qualified to teach what they are teaching. And there are teachers who are pompous and arrogant and fail to help a student understand complicated or new material.
All in all however, the greatest failure in education is the lack of support that excellent teachers get in order to do a proper job. I am now speaking primarily of public education. When a high school teacher has a computer graphics class and no computers, how can he teach? When a music teacher has no instruments, how can she teach? When an art teacher isn't given any books or supplies how can he teach? When there are 39 freshmen kids in an English class and only 30 chairs or desks, how can a teacher function? When a high school allows children into school who have no language skills and only went to the third grade in their previous country, how can they learn?
When a single dad is gone by 5:00am to his first of two jobs-- and it is the 9 year old's responsibility to get the 5 year old up and ready for the bus, where will dad be at homework time?
When a senior in high school gets up to go to school and her mom is hung over from the night before and can't drive her to school how successful will she be?
Karate Kid was a good movie...but real life is a lot more complicated than a well written script.