Sixty-nine children (20 with cerebral palsy (CP)) and their mothers participated in a joint writing activity. Children (M age = 64.56 months; SD = 7.07 months) wrote a four-item grocery list on a keyboard at home with their mothers. Mothers who had children with CP generally provided a lower level of graphophonemic (i.e., segmenting words into their respective sounds) and print support (i.e., identifying letters to type) when compared to mothers of children with typical development. They were also less likely to be playful and correct their children's writing errors, although they spent more time on the activity overall and entered into their children's physical space more frequently. Even when children's spelling skills were considered, mothers of children with CP provided lower levels of support to their children, suggesting that mothers might be missing opportunities to maximise what children with CP can learn during joint writing activities.