The stability of IQ in people with low intellectual ability: an analysis of the literature.

Whitaker (2008) pooled 42 earlier studies on IQ scores in people with low ability.

The meta-analysis covered 1,000-plus kids and adults with intellectual disability.

Most retest gaps were about three years and used Wechsler or Binet scales.

On average, IQ stayed very stable; the correlation was about .80.

Yet 14 percent of clients shifted at least 10 points up or down.

That one-in-seven chance is big enough to change a label or service plan.

Mazur et al. (1992) saw the same steady WAIS-R scores in the adults after 2.5 years.

Their small study is one piece Simon later rolled into the larger average.

Green et al. (2020) found Vineland-3 gives lower adaptive scores than Vineland-II.

Together the papers warn: scores can move when you switch tools or editions.

Expect IQ to hold for most clients, but schedule a fresh test before big decisions like classroom placement or guardianship. Pair the result with adaptive or wellbeing tools so a single 10-point swing does not steer the whole plan.