What elements of our society have the greatest effect on how our children develop?

I would say parenting is by far number one. Because parenting (or the lack of) is such a strong impact, that even the way someone else parents or doesn't parent their children ultimately could effect the way my children learn bad habits or good habits (influence). All the other options listed can also be controlled and limited by a good parenting method. Parents push education; media and technology is self explanatory; culture is learned from parents.

Was and always will be parenting. The problem is that lately, parents have abandoned their responsiblities. They have allowed day care centers, school teachers, grandparents, social media, video games, other kids...hell, just about everyone and everything else to "raise" their kids.

Culture includes education and the media (news and entertainment - well, maybe not so much news unless it comes through entertainment such as the Comedy Channel and celebrity pronouncements). Now, remember, you asked about the elements that have the greatest effect, not those which should have the greatest effect...