50% is a widely cited but seemingly outdated metric. Current research suggests that the vast majority of children with ADHD continue to experience it as an adult. This aligns with the NBME's position that "it has been shown that only 10% to 20% of children with the condition experience symptom remission in adulthood." (This is tested in CCSSA Form 14 Section 4 Question 15.)
"The MTA findings challenge the notion that approximately 50% of children with ADHD outgrow the disorder by adulthood. Most cases demonstrated fluctuating symptoms between childhood and young adulthood. Although intermittent periods of remission can be expected in most cases, 90% of children with ADHD continued to struggle with residual ADHD through young adulthood."
https://pmc.ncbi.nlm.nih.gov/articles/PMC8810708/
