This paper explores the way in which psychologists classified immigrant children as feebleminded through the use of intelligence testing and how state organisations consequently segregated them from public schools based on the scientific evidence. First, I show the way in which the psychologist Lewis Terman utilised intelligence testing to identify immigrant children deemed feebleminded. I focus closely on a survey and on his methodology and analysis. I then discuss the possibilities of education for the feebleminded and the segregation of immigrant children from regular classroom of public schools. Through his survey, Terman concluded that the exceptionally high ratio of feebleminded children in the tested region was caused by the large population of immigrant children, although the selection of the sample was often subjective, leading to "miscalculation" in his analysis. Terman's survey was influential in terms of segregating feebleminded children by stating their incurability; possibilities of education for the feebleminded were thus denied. At his suggestion, special classes and schools, along with a home for the feebleminded, were established. Terman's psychological survey was a cue for psychologists to enter the school system. The State Board of Education was not only attempting to discover the percentage of feebleminded children but also trying to apply psychology to school training. With the cooperation of the Board, the training of teachers for the feebleminded proceeded.