Well I had a lot of first hand experience with this stuff, growing up in one of the poorest places in the US.
I would say that roughly half the unsuccessful students I knew of were in fact very intelligent, the other half did seem to have lower intelligence. I knew a bunch of them well. Their home lives effectively wrecked them, hampered their learning habits, and their educational stacking progress - in which your knowledge builds year after year, and to succeed each year you must have a consistent rolling forward of that knowledge base from prior years. The unsuccessful but intelligent students had poor habits, poor role models, and often a terrible outlook. Some had been taught very backwards notions about how the world works, or what values should be pursued in life.
I don't think intelligence is a greater a factor than the others. I've known plenty of wildly unsuccessful, broken, smart people, that were crippled by a mediocre foundation at home. I've known successful low intelligence people, with discipline and a strong work ethic; people that can repeat patterns of success, while not having an especially great intellect.
I would say that roughly half the unsuccessful students I knew of were in fact very intelligent, the other half did seem to have lower intelligence. I knew a bunch of them well. Their home lives effectively wrecked them, hampered their learning habits, and their educational stacking progress - in which your knowledge builds year after year, and to succeed each year you must have a consistent rolling forward of that knowledge base from prior years. The unsuccessful but intelligent students had poor habits, poor role models, and often a terrible outlook. Some had been taught very backwards notions about how the world works, or what values should be pursued in life.
I don't think intelligence is a greater a factor than the others. I've known plenty of wildly unsuccessful, broken, smart people, that were crippled by a mediocre foundation at home. I've known successful low intelligence people, with discipline and a strong work ethic; people that can repeat patterns of success, while not having an especially great intellect.