Only very recently in Mexico sexual education is being part of the teaching at the public schools. Well, right off the bat, when an adolescent girl gets pregnant, she will be expelled from school. Regardless of what is fair, she will face a very, very difficult situation. There are many cases where the girl gets pregnant and the boy just runs away because he doesn't want to have anything to do with this now. In many cases, she will have to stay home, and do the familiar domestic work, and take care of things.
Adoption is another possiblility but is is still very uncommon in Mexico.
But I wouldn't say that that's the most frequent situation.