AbstractWhile errors on the WISC‐R are conceived primarily in terms of internal consistency and stability over time, examiners make mistakes that contribute to the inaccuracy of test scores. Studies to date mainly have investigated general scoring errors, rather than specific items most prone to error. Investigation of graduate students' test protocols indicated numerous scoring and mechanical errors that influenced the Full Scale IQ scores on two‐thirds of the protocols. Particularly prone to error were Verbal subtests of Vocabulary, Comprehension, and Similarities. More importantly, specific items on subtests in which numerous mistakes occurred were noted, as well as the most likely type of error for each item. These findings have implications for the education and training of assessment speciali