That number is likely under-reported, and there has been a significant rise in the number of people who feel comfortable identifying in the past few years. A study performed in 2017 found that 2.7% (of roughly 80,000 surveyed) identified as trans or gender non-conforming: https://pediatrics.aappublications.org/content/pediatrics/14...
I've seen the numbers that range from ~1% (or a little under) to as much as 3%, like the study above.
Gender non-conforming is a much wider net. This study you link of 9th and 11th graders, it is not surprising that a large percent (2.7% as you said) reported as trans or GNC.
The original comment above stated "trans", though, not T+GNC.
its not, its overreported. its trendy to change gender so people do it until theyre done with the phase. why do you think theres so many reports about people switching back and regretting their decision or going against their parents who forced them when they were younger?
I've seen the numbers that range from ~1% (or a little under) to as much as 3%, like the study above.