U.S. federal definition
A child exhibition one or more of the following characteristics to a marked degree for a long duration of time that adversely affects their education
1- Difficulty to learn that cannot be explained by intellectual, sensory, or health factors.
2- Difficulty to build or maintain satisfactory interpersonal relationships with peers and teachers.
3- Inappropriate types of behavior ( acting out against self or other ) or feelings (expresses the need to harm self or other, low self-worth, etc) under normal circumstances.
4- A general pervasive mood of unhappiness or depression.
5- A tendency to develop physical symptoms or fears associated with personal or school problems.