You may be surprised to learn that sex ed has no effect on teen pregnancy. American Journal of Public Health performed a meta-analysis on the roll out of sex ed classes in US states and found that 74% of studies showed 0% change and 26% showed sub-2% change.
Whether it's the religious abstinence-only teaching or a comprehensive course that includes all contraceptives. Both equally worthless.
The main driving factor from the 90s is that parents put pressure/guilt (The Talk) on their children earlier than ever now because of all the media scare about it.
I used to think it was the big spike in hormonal birth control for young teens, but Japan has almost no one on the pill and still has an ultra-low teen pregnancy rate so it's definitely not that.