A total of 51 Wechsler Intelligence Scale for Children, Fourth Edition (WISC-IV) protocols, administered by graduate students in training, were examined to obtain data describing the frequency of examiner errors and the impact of errors on resultant test scores. Present results were generally consistent with previous research examining graduate students' errors on the previous two editions of the WISC. Students committed errors on 98% of the protocols examined and averaged 25.8 errors per protocol. The most common errors were failure to query verbal responses, assigning too many points to an answer, and failure to record an examinee's response on the test protocol. Errors resulted in inaccurate test composite scores, with the Full Scale IQ and Verbal Comprehension Index most frequently affected. Error rates did not improve significantly over the course of three practice administrations. (Contains 4 tables.)