This study was designed to determine the psychometric properties of the School Readiness Assessment Tool (SRAT), a new measurement tool for assessing school readiness. The measure aims to assess preschool children's school readiness by estimating their academic, motor, social, emotional, and self regulation skills. Both academic and motor skills are assessed through direct child observation while teacher ratings evaluate social-emotional and self-regulation skills. 228 children attending preschool participated in the study's first phase and 185 children in the second phase. The results show that the items of the new measurement tool had sufficient internal consistency. Both study phases also showed strong evidence of face (content) and construct validity (i.e., convergent and concurrent validity). Overall, the results show that SRAT is a promising new measure for school readiness among preschoolers in Türkiye. In addition to the evidence from randomized control trials, studies should be conducted to determine its psychometric properties with diverse samples, such as rural children and children not enrolled in preschool education.