Based on the intersection of different systems at school entry, children and families often experience uncertainty about their preparedness and impending shift from other early childhood settings. This study used a mixed-methods explanatory sequential design and investigated the perspectives of parents and caregivers on kindergarten readiness with a focus on the impact of a summer kindergarten transition program in a southeastern state in the USA. A survey of 380 parents and caregivers within 30 randomly selected kindergarten classrooms and interviews with 10 parents and caregivers revealed informative findings. Based on the survey of the perspectives of parents and caregivers, children were more likely to demonstrate kindergarten readiness when they participated in the summer kindergarten transition program Countdown to Kindergarten (CTK), attended a preschool program, and were the first child to attend kindergarten in their families. Children were more likely to demonstrate kindergarten readiness when their parent and caregivers had more knowledge about kindergarten expectations and stronger relationships with the kindergarten teacher. The interview data revealed that CTK had a positive impact on child preparedness for kindergarten, parent/caregiver-teacher relationship, parent/caregiver involvement in school and class activities, and home learning. Parents/caregivers considered that CTK was of high quality, and they had different perspectives about their preferred number of visits and the location of visits. The findings can be used to inform the design and implementation of kindergarten transition programs as well as policy making in early childhood education and care.