My guess would be that Spanish-speaking immigrants are still immersed in their original culture, which is rooted in more traditional values. Primarily English speaking hispanics, on the other hand, have grown up in the sub-cultures that have developed around second and third generation children of immigrants. Many of those subcultures do not promote healthy world views and thus lead to the higher sexual activity.
Just a theory, anyway.
That sounds about right to me.
I think you've hit the nail on the head. My wife teaches in an inner-city middle school that is one-third black, one-third hispanic and one-third southeast asian. Despite being very passionately anti-illegal alien her favorite classes are the ESL hispanic classes. The black kids are generally thugs and "hos" as are the assimilated hispanic and southeast asian kids. You can't threaten those kids by saying that you'll tell their parents about their behavior because their parents (or mother I should say) doesn't care.
But the ESL kids are different. The parents are involved. She had the younger sister of a previous student and she told that student that her sister was always talking in class. "Jessica bad?" the ESL girl asked in her halting english. "Yes, Jessica bad," my wife responded. "OK, I tell my father. She not bad anymore," the girl answered.
My theory: TV, MTV.