Whether, and how, infant characteristics and parenting quality interact is one of developmental psychology's key questions. However, whether specific interaction patterns replicate across cohorts or developmental outcomes is largely unknown. This study investigates whether infant characteristics and parenting quality are independent predictors (additive effects) of child outcomes or interact such that certain infants particularly suffer from poor parenting (diathesis stress), particularly benefit from good parenting (vantage sensitivity) or both (differential susceptibility). Individual participant data from over 30,000 children from four prospective cohorts were pooled. Using a competitive-confirmatory approach of model evaluation, 16 possible permutations of infant characteristics (temperament and birthweight), parenting (maternal-reported stimulating and sensitive parenting) and later developmental outcomes (fluid and crystalised intelligence, internalising and externalising behaviour) were tested. The robustness of results was evaluated by subsequently varying analytic methods, using alternative parenting measures including observer reports and excluding covariates. AIC values in 10/16 analyses indicated infant characteristics acted independently of maternal-reported parenting for predicting developmental outcomes. Interaction patterns indicating diathesis stress (4/16), vantage sensitivity (2/16) or differential susceptibility (0/16) were rare or absent. However, diathesis-stress patterns were frequently found regarding birthweight and internalising behaviours, which were largely robust to methodological changes. Developmental outcomes are more consistently explained by additive effects rather than by interaction effects.