It's this one. Sample size was 2772 participants, the follow up period was in stages from age 10 to age 26.
https://link.springer.com/article/10.1007/s10508-024-02817-5
The majority of those who wanted to be the opposite sex in adolescence, no longer wanted to by early adulthood. 21% of all participants showed unhappiness with their sex in early adolescence; after adolescence only 2% of all participants continued to be unhappy with their sex.
The research results identified 3 cohorts from the study. First group of 78% displayed no 'gender non contentedness' throughout the study (from ages 10 to 26), the second group of 19% group reported gender non-contentedness in early adolescence, but not any longer in adulthood, and a third small group (2% of the sample) showed the opposite pattern of increasingly reporting gender non-contentedness with age.
"In addition, individuals with increasing or decreasing gender non-contentedness trajectories had lower global self-worth, more behavioral and emotional problems, and more often had a homosexual or bisexual orientation compared to individuals without gender non-contentedness..."
This is in keeping with data from the Tavistock. Most children referred to the gender clinics have a host of other stuff going on, especially autism, and many are same sex attracted.
This research suggests that if these children are not put on a medical or surgical pathway, feelings about their sex resolve. Perhaps it's partly because they come to terms with being gay - which fits in with the concerns of Tavistock staff who worried that they were transing gay kids.
In short, it's nuts to refer kids to gender clinics for an issue that will resolve in almost all if them if you let them mature.