Cognitive flexibility, the adaptation of representations and responses to new task demands, improves dramatically in early childhood. It is unclear, however, whether flexibility is a coherent, unitary cognitive trait that develops similarly across populations, or is an emergent dimension of task-specific performance that varies across populations with culturally variable experiences. Children from two populations that differ in pre-formal education experiences completed two distinct tests of cognitive flexibility, matched for complexity. Three- to 5-year-old English-speaking U.S. children and Tswana-speaking South African children completed two language-processing cognitive flexibility tests: the FIM-Animates, a word-learning test, and the 3DCCS, a rule-switching test. U.S. and South African children did not differ in word-learning flexibility, showing similar age-related increases. In contrast, only U.S. preschoolers showed an age-related increase in rule-switching flexibility; South African children did not. Working memory explained additional variance in both tests, but did not modulate the interaction between population-sample and task. The data suggest that rule-switching flexibility may be more dependent upon culturally-variable educational experience, whereas word-learning flexibility may be less dependent upon culturally-specific input.