I think it's 75, maybe 70. Actually, distant should know, I don't know why I'm replying.

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A full scale standard score of 69 on a measure of cognitive ability places an individual in the extremely low range. However, mental distinguished mentally-challenged is not determined by a mere IQ score, at least, not in Washington state.
For someone to receive services as an individual with mental distinguished mentally-challenged, they need to:
1. Display such a deficit in cognitive ability that their full scale standard score on a standardized measure such as the WJ-II Cog, WISC-IV, WAIS, SB-V is at or below 69.
2. AND demonstrate adaptive, social, and/or academic skill deficits.
So legally, if one were to have an IQ at 68 or below, BUT did not demonstrate skill deficits in their social, adaptive and/or academics, they would not be considered mentally distinguished mentally-challenged.