Parental involvement plays a vital role in the transition from kindergarten to primary school among children with intellectual and developmental disabilities (IDDs); this study aims to explore Chinese parents' experiences of parental involvement during this period. Informed by interpretive phenomenological analysis, semi-structured, one-on-one interviews were held with 10 parents. Three major themes were identified: (1) "aggressive" involvement; (2) factors in transforming parental involvement; and (3) "rational" involvement. Participants reported their perceptions, attitudes, and parenting behaviors in different phases of involvement in the transition to primary school. These findings highlight the need to support parents of children with IDDs during this time of change.