This study was undertaken to discover the effect of the Montessori Method on the cognitive tempo of 4–5-year-old children. Using an experimental pre-test–post-test paired control group design, the study sample included 60 children attending İhsan Doğramacı Applied Nursery School (affiliated to Selcuk University, Department of Health Sciences) in Konya during the 2015–2016 education year. The data of the study were collected using Kansas Reflection-Impulsivity Scale for Preschool–Form A. The tests were administered to children before and after the treatment and a follow-up test was administered to the treatment group six weeks following the completion of the treatment. The statistical analyses of the research data were done using Mann–Whitney U test and Wilcoxon Signed Rank Test. The results of the study indicated that the Montessori Method decreases the number of errors and extends the reflection time among the preschool children in the treatment group.