This paper reports on a study of parental involvement in children's mathematics learning in the context of a series of workshops carried out in four primary schools in the United Kingdom. Previous research suggests that, while there are high correlations between parental involvement and positive student outcomes, it can be difficult to raise student achievement via parental involvement interventions. We suggest that part of the reason for this, at least in relation to mathematics, is that parents experience considerable difficulties in negotiating school-centered definitions of and approaches to mathematics. We employed a design and analytic approach informed by Derridean concepts including decentering and différance. We encouraged parents to work with their children to "find the math" in everyday life and activity. A significant component of the discussion in each school involved sustained, critical reflection about the meaning of "mathematics" and about parents' interpretations of parental involvement in children's education. We made sense of parents' discussions during the workshop by offering an account whereby parents grappled with mathematics as a socially constructed domain, dominated by school-centered ideology. As parents became more confident in their own analysis of the mathematics in everyday family life, they developed new strategies for sharing this mathematical thinking and awareness with their children. Implications for school parental engagement strategies are discussed.