Early childhood years are significant for the development of young children and for later life. Children’s school readiness is an integral part for their holistic development consisting of physical well-being, social and emotional development, cognitive and language skills, understanding of the world, mathematical skills, and creative arts and so on. Given the scarcity of empirical studies on early years of children’s school readiness transitioning to primary education globally and specifically in the context of Pakistan, this study sought to explore early childhood education (ECE) and grade I teachers’ perceptions regarding school readiness for children’s transition to private schools across Karachi, Pakistan. A cross-sectional survey was carried out within the quantitative research paradigm. A total of 275 (162 ECE and 113 grade I) teachers selected through stratified random sampling technique, participated in the study. To fulfill the purpose of the study, a contextually relevant tool was developed, based on six key learning areas stated in the National Curriculum for Early Childhood Education (NC for ECE) 2017 for school readiness. A descriptive analysis was employed and the non-parametric ‘Mann Whitney U test’ was applied to explore the differences or similarities between the ECE and grade I teachers’ perceptions. The findings of the study reveal that both ECE and grade I teachers highly regarded all the competencies stated in NC for ECE 2017, as fundamental for young children’s school readiness. The results of the comparisons between these two groups of teachers were not significant for all six key learning areas. Whereas one comparison was significant (p = < 0.014) for the competency within Basic Mathematical Concepts i.e. number operations. This implies that grade I teachers regarded number operations more important for children starting grade I as compared to ECE teachers. The results of the study show that the similarities and differences in teachers’ perceptions suggest that opportunity must be provided to ECE and primary teachers to meet together to discuss the NC for ECCE for its effective use and also for the vertical alignment of curriculum. The study recommends further research in this area, especially qualitative inquiry for an in-depth understanding of school readiness, its opportunities and perceived challenges in the context of private schools in Karachi, Pakistan.