Significant interference with functioning. It would be difficult to argue that a child making B's and earning good conduct marks is having significant problems. In contrast, it is a matter of concern when a child regularly fails to turn in homework that has been completed. Not explainable by any other disorder. Children with learning disorders often struggle to put their minds to work on tasks that are simply more difficult for them.
Inattention is also a common symptom of both depression and anxiety.
Anxious or traumatized children often demonstrate hypervigilance which can be mistaken for distractibility. Children from chaotic family histories may not have learned the self-control needed to attend in structured classrooms. This is not to fail to note that some children are simply disruptive because they are disobedient. These point to an area of the brain called the orbital-frontal region, along with some of its neural connections to other places, particularly in the right hemisphere. It appears that these differences are attributable to lower levels of dopamine, one of the chemicals used by the brain in transmitting messages from one area to another.