This study examined the consequences of negative change in mothers' implicit appraisals of their adolescents after engaging in a family disagreement. Participants included 194 mothers and their early adolescents (M[subscript age] = 12.4 at Wave 1; 50% female) followed over 1 year. Mothers' implicit appraisals of her child as "unlovable" were assessed using the Go/No-Go Association Task--Child (Sturge-Apple, Rogge, Skibo, et al., 2015), an associative word-sorting task, before and after engaging in a family conflict task. Mothers' implicit appraisals, on average, did not become more negative following conflicts with their teen. However, substantial variability was evident, suggesting that important individual differences exist in mothers' cognitive reactivity to conflict. Greater susceptibility to implicit change predicted more harsh and insensitive parenting in response to their adolescents' bids for support 1 year later. This effect held over and above mothers' emotional reactivity to the conflict, their explicit negative attitudes about their adolescent, and maternal harshness at Time 1. Harsh and insensitive parenting, in turn, mediated the link between maternal implicit reactivity and subsequent increases in adolescent internalizing and externalizing problems. The results suggest that individual differences in maternal susceptibility to changes in implicit appraisals following conflictual interactions serve as a unique determinant of parenting in adolescence.