There don't seem to be that many good studies on IQ among the Amish - though Amish schools do frequently give their students standardized tests as a way of keeping the government at bay; more on that later - but I did manage to find one study from 1969 by John A. Hostetler et al, published in the book "Children in Amish Society: Socialization and Community Education." The study estimated IQs based on the SRA Tests of Educational Ability as well as the Goodenough-Harris Draw-A-Man test for Amish students in grades 5, 6, 7 8, as well as for a control group of rural public school children in grade 8. Below are the comparisons for the Amish in 8th grade (N=115) and the control group (N=61) based on the SRA Tests of Educational Ability:
|Mean IQ Scores of Amish Pupils and Control Group in Grade 8, SRA Tests of Educational Ability|
The authors state that the difference in composite IQ scores was not statistically significant. However, one thing that jumps out in this table is how much lower the Amish scored on the language subtest relative to the control group - a result which was repeated in another test the researchers administered, the Iowa Tests of Basic Skills, which did not estimate IQ directly. The researchers give two possible explanations, each of which suggests that the result is not due to an actual deficiency in native verbal intelligence on the part of the Amish cohort:
"The generally low performance of the Amish on the language aspects of the two tests described above can perhaps be attributed in part to the time limitation. On rechecking the reading tests we found that the children did very well in the part they finished; but, especially in the upper grades, most of the children who had not been trained to take timed tests did not complete the work. It should also be remembered that English is a second language that is not learned until they enter school."
I'm skeptical of the first explanation, but find the second one to be fairly plausible. Amish children generally speak Pennsylvania Dutch at home, and a significant part of their schooling (Bible study) is conducted in German.
Results from the Goodenough-Harris Draw-A-Man test suggest that Amish children have average or above average non-verbal intelligence relative to other whites. The test was administered to 389 students aged 6 through 15 in Amish schools. Mean IQ for Amish children was 101.6 relative to the U.S. mean of 100. Furthermore:
"The 12 schools ranged from a low [of] 91.5 to a high of 112.7. The achievement in this test in the various Amish schools paralleled the degree of taboo against representing the human figure in various communities."
This suggests that the aggregate score underestimates non-verbal intelligence among the Amish, the accurate measurement of which is compromised in some sects by the fundamentalist Christian prohibition against creating graven images.
All in all, the Amish seem a relatively intelligent population, which is perhaps what one would expect given their German-Swiss origin.
Hostetler, John A. et al., "Children in Amish Society: Socialization and Community Education," Case Studies in Education and Culture, Holt, Rinehart and Winston Inc., 1971. Pages 91 - 95.