A set of 5 reaction time tests of increasing cognitive complexity were administered to 35 secondary school pupils in Zimbabwe and The Netherlands at 4 consecutive school days in order to explore the existence and nature of cross-cultural differences on reaction time tests measuring basic cognitive operations. No cross-cultural differences were observed on the simple tests, while the Dutch pupils were faster than Zimbabwean pupils on the more complex tests. Zimbabwean pupils showed larger performance increments at retesting. Two Wechsler Intelligence Scale for Children (WISC) subtests (Vocabulary and Digit Span Forward and Backward), a tapping test, and parental socioeconomic status were used to predict the cross-cultural performance differences. Socioeconomic status and digit span could explain all these differences. It is argued that the cross-cultural performance differences on elementary cognitive tests cannot be interpreted at face value because of their susceptibility to non-target factors, such as test understanding and previous test exposure. (Contains 4 figures and 5 tables.)