Don't think so. I think every person is born with a certain amount of potential. All the encouragement and education in the world will only allow that person to get closer to his maximum potential. It cannot be exceeded.
That noted, it is VERY easy to keep even someone with a great deal of potential from achieving: teach an explicit or implicit ideology of not trying, malnutrition, lack of education, actual oppression, etc.
Think of it this way. Every person is born with a genetic potential to achieve a given height. It can be stunted by malnutrition and other factors. But it doesn't matter how well he is fed, he cannot exceed that genetic potential.
Or raise them to be vareer victims. Didn't anyone actually read the article?
The only limitation to potential is that which we impose on ourselves. There are many examples of people surpassing all expectations throughout history.
A person's level of success will be a combination of nature and nurture. If a person's "nurture" score would be 2 out of 100, however, I'm not sure how much it matters whether their "nature" score would be 10 or 90. The highest levels of success would be out of reach for most people, no matter how well they were raised, but a person of average intelligence raised well could likely outperform a much more intelligent person who was raised badly.