This paper presents the findings of a study conducted with preschool teachers trialling an intervention in which executive function activities are embedded in teachers' daily practices and imaginary play is used to build meaningful problem situations that children solve using executive functions. The participants were 227 preschool children (53% male, M age = 55.5 months, SD = 4.2) in 10 preschool groups from Brisbane, Australia. The intervention consisted of educators and children creating and developing an imaginary situation (playworld) over an extended period (e.g. one school term). Executive function was assessed pre- and post-intervention. A repeated measures ANOVA demonstrated significant differences between Time 1 and Time 2 on all executive function measures. The study found that teachers can develop children's executive functions when executive function activities are embedded in teachers' daily practices, and when imaginary play is used to build meaningful problem situations that children solve using executive functions.