The brain of a child develops rapidly throughout the years, but there are critical periods of development in which the brain is particularly active and certain skills or functions hit their milestones. When a developing brain is injured, the damage to the brain may limit or delay these milestones.
Much research has focused on the most critical ages of childhood development. In terms of brain injury, a recent study suggests that the most critical age range in development is 7-9 years old. When compared to children age 6 and under or children age 10 and older, the 7-9 year olds were the most vulnerable to poor outcome following brain injury. Poor outcome was associated with lower IQ scores.
The researchers theorized that ages 7-9 may be the time when critical skills such as time management, reasoning, task planning, and impulsivity control are milestones in development. A deficit in these critical skills can lead to overall deficits in IQ, as well as school performance, speech development, and social skills.
Crowe LM, Catroppa C, Babl FE, Rosenfeld JV, & Anderson V. Timing of traumatic brain injury in childhood and intellectual outcome. Journal of Pediatric Psychology. (July 2012).