DSM croteria, although this is being reviewed ATM. Assessment can be amde by psychs, utilisation of medical testing tools or increasingly through the use of tools such as 3Di which invovle inutting assessments of profesionals and aprents into an IT absed algorhythm based system.
Diagnostic Criteria
Diagnostic criteria for Attention-Deficit/Hyperactivity Disorder:
A. Either (1) o r (2):
(1) six (or more) of the following symptoms of inattention have persisted for at least 6 months to a degree that is maladaptive and inconsistent with developmental level:
Inattention
(a) often fails to give close attention to details or makes careless mistakes in schoolwork, work, or other activities
(b) often has difficulty sustaining attention in tasks or play activities
(c) often does not seem to listen when spoken to directly
(d) often does not follow through on instructions and fails to finish schoolwork. Chores, or duties in the workplace (not due to oppositional behavior or failure to understand instructions)
(e) often has difficulty organizing tasks and activities
(f) often avoids, dislikes, or is reluctant to engage in tasks that require sustained mental effort (such as schoolwork or homework)
(g) often loses things necessary for tasks or activities (e.g. toys, school assignments, pencils, books, or tools)
(h) is often easily distracted by extraneous stimuli
(i) is often forgetful in daily activities
(2) six (or more) of the following symptoms of hyperactivity-Impulsivity have persisted for at least 6 months to a degree that is maladaptive and inconsistent with developmental level:
Hyperactivity
(a) oft en fidgets with hands or feet or squirms in seat
(b) often leaves seat in classroom or in other situations in which remaining
seated is expected
(c) often runs about or climbs excessively in situations in which it is inappropriate (in adolescents or adults, may be limited to subjective feelings of restlessness)
(d) often has difficulty playing or engaging in leisure activities quietly
(e) is often ?on the go? or often acts as if ?driven by a motor?
(f) often talks excessively.
Impulsivity
(g) often blurts out answers before questions ha ve been completed
(h) often has difficulty awaiting turn
(i) often interrupts or intrudes on others (e.g., butts into conversations or games)
B. Some hyperactive-impulsive or inattentive symptoms that caused impairment were present before age 7 years.
C. Some impairment from the symptoms is present in two or more settings (e.g. at school [or work] and at home).
D. There must be dear evidence of clinically significant impairment in social, academic, or occupational functioning.
E. The symptoms do not occur exclusively during the course of a Pervasive Developmental Disorder, Schizophrenia. or other Psychotic Disorder and are not better accounted for by another mental disorder (e.g., Mood Disorder, Anxiety Disorder, DissociativeDisorder, or a Personality Disorder).
Am a bit 
actually as first time I have read it and ds2 meets EVERY criteria on there. Fuck.