Hazel, GREAT, SUCCINCT answer! Here is my synopsis of the question.People with higher levels of education & corresponding IQ levels know the importance of family planning.They contend that children in small families(1-2 children) have THE BEST educational & socioeconomic opportunities.They realize that children need individualized parental attention, care, & love which will be non-existent if they had large/very large families.
People with higher levels of education & IQs are aware that small families insure families of a civilized, higher qualitative standard of living which is missing in the large family environment where constant poverty & struggle are normative lifestyles.They also are cognizant that small families create a more harmonious atmosphere for both husband & wife as well as children.They realize that there is LESS STRESS in the small family environment than there is in the large/very large family environment.
People with higher levels of education & IQs know that small families are conducive to children's self-esteem & intellectual development. There was a study done by Dr. Zajonc, social psychologist, which confirm that the larger the family, the less intellectually mature & developed children are because they teach & raise each other & there is little or no adult interaction in large/very large families.Highly educated & intelligent people realize that adult interaction is of paramount importance in a child's development & in small families, children have more chances to interact with adults than children from large/very large families who primarily interact with each other.
People with lower educational & IQ level aren't cognizant of family planning methods.In fact, they are distrustful of family planning & birth control methods.Many of them believe that birth control & family planning are unnatural. They view having large/very large families as an inevitable part of life.They have a very passive purview of having children. Their purview is to let it rip.
Also people with lower educational & IQ levels, particularly the women, have very limited options as far as their life goes.They have no outside hobbies so they see having children as filling whatever void they have in their lives. They even use being pregnancy as a means of receiving the attention they would not achieve otherwise. Many men who are less educated & intelligent view having a large/very large families as a way to assert their masculine status.