The article employs the model of executive functions by A. Miyake to preschool age. The main objective of the research was the approbation of the diagnostic instrument NEPSY-II to assess the level of development of the three main components of executive functions (working memory, cognitive flexibility and inhibition) in the Russian preschoolers. The sample consisted of 267 children (143 boys and 124 girls) aged 5–6 (M = 5.6, SD = 0.3), who frequented the senior group of Moscow nursery schools. In the result of comparison of the performance of American and Russian children aged 5–6 years, certain cross-cultural differences were found: remembering images in general is more developed in Russian children, while spatial memory is better in American kids. To verify the convergent validity of the instrument on a partial sample (N = 48), correlation analysis was conducted of the results of two batteries of tests: one that was approbated and one by L.A. Venger. The found correlations confirmed the feasibility to use this instrument for the executive functions assessment. The data analysis showed that the levels of audio-verbal and visual working memory in senior preschoolers are not connected. But audio-verbal working memory is at large the foundation of the development of cognitive flexibility (switching), while visual working memory underlies the inhibition. Based on the results of the assessment four variants of executive functions in senior preschool age were distinguished and described. Children with relatively high level of development of executive functions were arranged in two groups in accordance with orientation: those who sought to perform the tasks faster and those who were focused on quality (avoidance of mistakes).