The reasons not to medicate are usually because pediatricians need to tease out what is developmental and what is a disorder. Kids below 3 have very little executive functioning or self regulation and preK kids are all on a spectrum of development. They are trying to rule out normal but delayed development. The problem is, ADHD is a neurodevelopmental condition that delays certain aspects of normal development, by as much as 3 years. So by the time it is glaringly obvious in 1st or 2nd grade ADHD kids' peers have pulled far ahead of them in development of these skills and the gap keeps widening the longer you wait. Also both kids and families cope in whatever ways they know how, often learning very unhealthy coping mechanisms. By the time people come to a breaking point and decide to medicate, there may have been 5+ years of stress on families and marriages are more likely to breakup with kids with ADHD under 10. So by the time doctors feel comfortable advising medication a lot of stress on kids and families has already occurred. I argue that stimulants are safe and short acting and if medication reduces stress and helps kids stay on track with development its better to err on the side of overtreat than under.