Researchers have found that the difference in age is important. The younger the child, the more likely the child is to score poorly on standard tests. And, the more likely the child is to be taking prescription drugs for behavioral problems.
For example, a school system may say any child who turns six during a calendar year starts school that September.
When school starts in September, a child born in January will have been six years old for nine months while a child born in December will be five years and nine months old.
One child is 81 months old and the other is 69 months old, a difference of about 17 percent in age. This is a very large difference in stages of maturity and development.
Experts cannot say the difference in age is the reason more behavioral drugs are given to younger children for attention deficit hyperactivity disorder (A.D.H.D.). One doctor said, “It may be that the youngest kids in the class are just acting according to their age. But their behavior is thought of as symptoms of something else, rather than lesser maturity.”
The difference in school performance associated with age is less evident for girls. For both girls and boys, differences lessen but continue as they get older.