Simcha is defending teaching cycle-charting to the unmarried, including teens, here:
"I was in college and unmarried when I first even heard about NFP. I was a fairly new Catholic and I knew the Church opposed artificial contraception but it took a while before I found out that there was any kind of effective family-planning alternative. (Somehow, they never covered this in RCIA—either that the Church opposed contraception or that any licit recourse existed for married couples who judged it prudent or necessary to space children).
As you can imagine, the months between finding out (a) that contraception was not, in fact, an option ever and (b) that NFP exists were somewhat freaked-out ones.
When I did learn about NFP, probably from the little baby internet we had back then, my first thought was: “You have got to be kidding me! I have to try this!” Sort of in a “how cool is that?!” sense. So I tried to order a copy of a NFP textbook from a nationally known NFP teaching organization, and they wrote me back to tell me it was a BAD IDEA for a young unmarried woman to fall into the temptation of knowing how her cycles worked.
I knew perfectly well where to get free condoms—I was a state university student, after all, they practically leave them like mints on your pillows at the dorm—so I concluded that whatever assumptions the NFP teaching org adviser was making didn’t apply to me, and persisted in my search to find out how to do this cool trick where you could find out when you would have your period.
So I went to the library, where I found a slightly out-of-date edition of the same textbook (hint: it had daffodils on the cover), made myself a chart in Microsoft Excel, and about seven weeks later experienced the twin sensations of WOW IT WORKED THAT IS SO COOL and I HAVE BEEN LIED TO MY WHOLE LIFE ABOUT MY OWN BODY. The experience was faith-strengthening. I continued to chart until I was married several years later."
I am still about 6 years away from my second trip through female puberty, but it probably won't surprise you that I am an advocate of teaching young people about NFP in adolescence. The details aren't worked out yet, though, and so far none of the kids have thought to ask about the charts on the bathroom counter, which I would be too lazy to hide even if I were of a mind to hide them.
(That is probably an exaggeration. I manage to put them away every month before the house cleaners come.)