The ability to override habit and exercise conscious control over thought, emotion and action, termed `executive function' (EF), is a defining feature of human cognition. While a great deal is understood about the underlying cognitive processes and neural substrates of EF, much remains unknown about how it develops. Conflict monitoring theory has emphasized the role of prefrontally-based conflict monitoring and detection mechanisms in the activation of control processes. In contrast, Vygotsky's sociocultural theory of development suggests that experience, especially language, plays a key role in the emergence of higher-cognitive functions like EF from more basic cognitive processes. Both of these accounts have received broad empirical support, but they have never been considered in relation to one another. The current research tested the hypothesis that linguistic experience plays a key role in the development of conflict detection and EF. Study 1 tested the prediction that children who notice and focus on contrasting states of affairs show better EF. A significant relation was found between three-year-old children's EF and their tendency to focus on contrast indexed by their use contrastive negation on a novel picture book task, controlling for age and verbal IQ. In Study 2, a training experiment was conducted using a pre-post control group design in which three-year-old children were provided with linguistic experience involving the use of negation to contrast objects, attributes, and actions, and change in EF performance on a battery of EF measures was assessed. Results indicate that children exposed to contrastive negation showed greater increases in EF from pre- to post-test compared to children in two control conditions: an active control condition that experienced the stimuli without contrastive negation, and an inactive control condition in which children were read storybooks. Taken together, these findings provide new evidence that linguistic experience with contrastive negation used to highlight incompatibility may play a key role in the development of EF by increasing children's sensitivity to conflict, and possibly also by facilitating inhibition of task-irrelevant representations. Implications for theories of EF are discussed.