may be much lower than nonverbal ones, particularly in preschool and school-age children. As a result, overall indices of intellectual functioning may be misleading (Ozonoff and Miller, 1995). Second, correlations reported in test manuals between various assessment batteries may not readily apply, although scores often become more stable and predictive over time (Lord and Schopler, 1989a; Sparrow, 1997). Third, for some older children with autism standard scores may fall over time, reflecting the fact that while gains are made, they tend to be at a slower rate than expected given the increase in chronological age. This drop may be particularly obvious in tests of intelligence that emphasize aspects of reasoning, conceptualization, and generalization.

Approximately 10 percent of children with autism show unusual is-lets of ability or splinter skills. These abilities are unusual either in relation to those expected, given the child’s overall developmental level, or, more strikingly, in relation to normally developing children. The kinds of talents observed include drawing, block design tasks, musical skill, and other abilities, such as calendar calculation (Treffert, 1989; Shah and Frith, 1993; Prior and Ozonoff, 1998). Hermelin and colleagues (e.g., Hermelin and Frith, 1991) noted that these unusual abilities may be related to particular preoccupations or obsessions. Such abilities do not seem to be based just on memory skills; they may reflect other aspects of information processing (Pring et al., 1995).

In summary, general measures of intellectual functioning, such as IQ scores, are as stable and predictive in children with autistic spectrum disorders as in children with other developmental disorders, but this does not mean that these measures do not show individual and systematic variation over time. Because IQ scores provide limited information and there are complex implications of test selection across ages and developmental levels, IQ scores should not be considered a primary measure of outcome, though they may be one informative measure of the development of the children who participate in an intervention program. Specific cognitive goals, often including social, communicative, and adaptive domains, are necessary to evaluate progress effectively. Direct evaluations of academic skills are also important if children are learning to read or are participating in other academic activities.

Various theoretical notions have been advanced to account for the cognitive difficulties encountered in autism. The “theory of mind” hypothesis proposes that individuals with autism are not able to perceive or understand the thoughts, feelings, or intentions of others; i.e., they lack a theory of mind and suffer from “mind blindness” (Leslie and Frith, 1987;