It is facile to define links between sexual education and pregnancy rates; people with lower incomes historically have been more prolific, for want of education.
Not that simple.
They are prolific for many other reasons, all beginning and ending with a dearth of hope and opportunity. They don't believe life can get worse. They also don't believe it can get better. They don't believe anything they do will make much of a difference, and they're correct.
It should be noted that "prolific" means "fruitful" (ie, having a lot of offspring, not aborting them), but perhaps you meant profligate or promiscuous or something.
Which is also applicable to the poor. They have more indiscriminate sex than the rich. They have more kids than the rich. They also have more abortions than the rich.
All the reasons come back to the same thing.
Not "lack of education". Lack of opportunity. Some grow up in such a mentally, intellectually, emotionally, and spiritually impoverished environment that they would not be able to
utilize an opportunity even if it were handed to them. They would not be able to use, for instance, a full scholarship to college, if they are functionally illiterate.
There is little about the world that they understand, some of them. They don't understand how things work, and aren't capable of learning, because they have no foundation and no context for such knowledge. They are very isolated, alienated, and disenfranchised from the larger world, although aware of it.
They do understand sex, and children, and families, however, no matter how disadvantaged and underprivileged they are.
They understand these things as positive, and within their grasp, unlike much of anything else.