honestly, if i hear that 80% figure thrown about one more time, I'm going to scream. They're basing that figure on gender non-conforming children, not trans children exclusively. I'm talking about the ones with insistent, consistent, and persistent gender dysphoria. Our gender identity is set by the 6th month of gestation, asking a transgender 12 year old to wait until they are 16 before starting hormones does more harm than good.

Zucker did that study, and I trust him as far as I can throw him Perhaps the clearest evidence that most children in these samples were never transgender to begin with is that, when they were directly asked “are you a boy or a girl” as part of a battery of intake questions, an overwhelming percentage (more than 90 percent) of children in these clinics provided the answer that aligned with their natal sex. Is it so surprising that the majority of boys who in childhood believed themselves to be boys in adulthood believed themselves to be men? As one research team based in Amsterdam concluded: “[E]xplicitly asking children with GD [gender dysphoria] with which sex they identify seems to be of great value in predicting future outcomes for both boys and girls with GD.” That is, even within samples of gender nonconforming children, the ones who say they are the other gender are the ones who are most likely to say the same thing later in life.

here
http://www.slate.com/blogs/outward/2016/01/14/what_alarmist_articles_about_transgender_children_get_wrong.html