Despite low to moderate convergent correlations, assessment of youth typically relies on multiple informants for information across a range of psychosocial domains including parenting practices. Although parent–youth informant discrepancies have been found to predict adverse youth outcomes, few studies have examined contributing factors to the explanation of informant disagreements on parenting practices. The current study represents the first investigation to concurrently examine the role of mother and son’s self-reported affective dimensions of temperament and depression as pathways to informant discrepancies on parenting practices. Within a community sample of 174 mother–son dyads, results suggest that whereas mother’s self-reported temperament evidenced no direct effects on discrepancies, the association between the product term of mother’s negative and positive temperament and discrepancies on positive parenting was fully mediated by mother’s depression (a mediated moderation). In contrast, son’s self-reported temperament evidenced both direct and indirect effects, partially mediated by depression, on rating discrepancies for positive parenting. All told, both son’s self-reported affective dimensions of temperament and depression contributed to the explanation of discrepant reporting on parenting practices; only mother’s self-reported depression, but not temperament, uniquely contributed. Results highlight the importance of considering both parent and youth’s report in the investigation of informant discrepancies on parenting practices.