READING-DISABLED STUDENTS WITH AND WITHOUT COMORBID ARITHMETIC DISABILITY

Two subgroups of learning disabled students, reading disabled only (RD) and reading/arithmetic disabled (RAD), were contrasted at two age levels, 8 to 12 years old and 12 to 17 years old. At both age levels, RAD students were significantly poorer spellers and weaker on the Arithmetic and Coding subtests of the Wechsler Intelligence Scale for Children (WISC) than RD-only students, The younger subgroups were also differentiated by four other WISC-R subtests: Information, Similarities, Comprehension, and Block Design. The adolescent subgroups differed on the new Symbol Search subtest of the WISC-III. The subgroups did not differ at either age level on phonological skills, memory tasks, naming speed, and picture vocabulary. Nor did they differ on parent ratings of externalizing and internalizing behavior problems. Evidence is presented that arithmetic disabled children fall relatively further behind with increasing age. A core weakness in reading and arithmetic disability is processing speed, and students with dual disabilities are particularly impaired. Other possible factors in co-occurring reading and arithmetic disability are inferential reasoning, generalization, temperament, and inadequate supervised practice.