Speech and language therapists' (SLTs) roles include enabling parents to provide intervention. We know little about how parents understand their role during speech and language intervention or whether these change during involvement with SLTs. The theory of conceptual change, applied to parents as adult learners, is used as a framework for understanding changes in parents' conception of roles during intervention. The aims of the study were (1) to investigate parents' conception of their own and SLT roles during speech and language therapy intervention and (2) to explore changes in parents' conception of their role as they work with SLTs. A qualitative study was conducted using semi-structured interviews with 14 parents of pre-school children with speech and language needs referred to speech and language therapy in the UK. A subset of 8 parents participated in a longitudinal study over nine months to track any changes in conception of roles during intervention. Interviews were analysed using Thematic Network Analysis to identify basic, organizing and global themes. Framework Analysis was used to compare participants over time and identify any changes reported by parents. Parents had a firm conception of their role as advocates but did not express a clear notion of their role as intervener before involvement with the SLT. During intervention, some described changing their conception of role including adopting roles as "implementer" and "adaptor" of intervention. In some cases, parents described changes in their approach to parenting which they associated with adopting more active roles as interveners. Policy statements about parental choice and co-working typically present parents' conception of roles as fixed. This research shows that parents may change their conception of role as they work with SLTs and become increasingly involved as interveners. Implications for practice include negotiating roles in the partnership before intervention begins and enabling parents to adopt an intervener role.