Well--here's a criteria list for you, from a site I won't link to due to the fact that it contains ads, but a Google search can give you the citation.

Diagnostic criteria for Mental Retardation



A. Significantly subaverage intellectual functioning: an IQ of approximately 70 or below on an individually administered IQ test (for infants, a clinical judgment of significantly subaverage intellectual functioning).

B. Concurrent deficits or impairments in present adaptive functioning (i.e.. the person's effectiveness in meeting the standards expected for his or her age by his or her cultural group) in at least two of the following areas: communication. self-care, home living, social/interpersonal skills, use of community resources, self-direction, functional academic skills, work, leisure, health, and safety.

C. The onset is before age 18 years.

Code based on degree of severity reflecting level of intellectual impairment:



317 Mild Mental Retardation: IQ level 50-55 to approximately

318.0 Moderate Mental Retardation: IQ level 35-40 to 50-55

318.1 Severe Mental Retardation: IQ level 20-25 to 35-40

318.2 Profound Mental Retardation: IQ level below 20- 25

319 Mental Retardation, Severity Unspecified: when there is a strong presumption of Mental Retardation but the person's intelligence is untestable by standard tests

I have to say, though, that nowhere did I learn that having difficulty learning morality or ethics was the primary symptom of retardation. It is virtually always part of an array of symptoms...when it is tied to retardation.

There are plenty of people of average or high intelligence who have difficulty with morality or ethics ; sociopaths are the extreme.

Rats! Thought I could put a link for you, but no. If Google will take you to The Free Dictionary, look up Antisocial personality disorder; you will find many terms fitting various levels. One of these may be the one you're looking for.