her work of administering binet intelligence tests at the clearing house primed her for work with the gifted, and naturally with the mentally defective as well. hollingworth also performed research on this other side of the intelligence spectrum as well. she learned, through working with mentally defective children, that many of them actually had normal intelligence. yet, these children were suffering from adjustment problems during adolescence. from this discovery she began to focus more on this population. she published several books on the topic: "the psychology of subnormal children" (1920, "special talents and defects" (1923) and "the psychology of the adolescent" (1928). the last of these became a leading textbook for the following two decades. it even replaced one written by g. stanley hall. several magazines noted the importance of the book and published excerpts from the chapter, "psychology weaning." the book gives several examples of this psychological process in which it is successfully completed in order to guide puzzled parents and aid them with their children. she describes it as similar to the "physical weaning from infantile methods of taking food, it may be attended by emotional outbursts or depressions, which are likely to come upon people whenever habits have to be broken." additional writing done on children with mental defects can be found in her books, "the problem of mental disorder" (1934) and in "psychology of special disability in spelling" (1918). she even wrote her own textbooks for the classes she taught at columbia.