Genetics is not so much the factor as child rearing is. The way we raise our children is the single most important factor in how successful they'll turn out to be. A child must be thought social skills for example in order to succeed in an educational environment.
Stupidity is subjective and does not define an individual or group. A stupid person is defined by other individuals. Those other individuals do not know all, therefore they are in their own rights stupid. People who cannot nurture a child should make the responsible decision to wait until they can.