Yes it is, with children that were raised the old fashioned way from birth and do not suffer a chemical difference in the way their brain works.
However, there are studies of children, for example, who spent significant baby/toddler time in institution settings such as orphanages, that actually show a difference in brain function. There seems to be some evidence that neural connections are not developed the same way in children suffering that sort of neglect. A huge number of PI )post-institutionalized) kids are ADD/ADHD. This is not merely a behavior issue, but a neurologic difference. The ADHD meds for these children actually help compensate for the physiologic difference, and offer such children the ability to attend, control and actually learn. The med result is NOT zombi-ism, it is a compensation which balances the child into the same state as a child who is not ADD. ADD is not merely a lack of discipline, it is a difference in how the child's brain works. The ADD meds bring them the same ability to physically control movement and reaction that their non ADD peers already have. My daughter is a dynamo. Very bright, very active, and was very severly delayed (NO language development at age 2 when she came to us) and had extreme inability to attend- partially due to the impact of her PI beginnings. She is far from zombie-like on her ADD meds. The difference off-meds is severe in the classroom-she can't concentrate, she can't sit, she can't attend and she can't learn. And is very impulsive. The "discipline" she gets has nothing to do with it. If it were merely lack of discipline, being off-meds would make little difference in behavior- because she has recieved the same discipline.
Properly dosaged ADD meds to children is comparable to them as insulin is to a diabetic child. It is balancing out an imbalance in their system.
AS a matter of fact, my daughter was so severe off-meds that she was at first misdiagnosed as bipolar. She is on a very low dose of a timed release new generation of ADD meds called Adderall, and at 5 pm or so as the meds wear off, you can just SEE the difference in her. On-meds, she is not a zombie, she is a normal child. off meds shes nearly manic.