Almeida, RitaBarros, LuisaSantos, MargaridaBeeghly, MarjorieFuertes, Marina2026-03-092026-03-092026Almeida R, Barros L, Santos M, Beeghly M, Fuertes M. Involvement in Portuguese father-infant free play interactions at 3 and 9 months. Parent Sci Pract. 2025 December 30. Epub ahead of print.http://hdl.handle.net/10400.21/22701This work was supported by Grant UI/DB/151103/2021 from FCT—Fundação para a Ciência e a Tecnologia, I.P., through the Research Center for Psychological Science of the Faculty of Psychology, University of Lisbon; Fundação para a Ciência e Tecnologia [2022.07322.PTDC].Objective. Although continuity and stability in parental sensitivity promote a sense of security and predictability for infants and are linked to a variety of positive child outcomes, research with fathers is relatively rare. The present Portuguese longitudinal study investigates mean group-level continuity (vs. discontinuity) and individual-order stability (vs. instability) of ratings of paternal sensitivity and other dimensions of father-infant interactive behavior with infants from 3 to 9 months. Design. Participants included 61 urban middle- to lower-middle-class Portuguese fathers and their healthy, term infants observed during free play at 3 and 9 months. Multiple dimensions of paternal and infant behavior were scored using Crittenden’s CARE-Index. Fathers also reported on their involvement in childcare activities using the Parents’ Responsibility Scale. Results. The magnitude of fathers’ average group-level sensitivity decreased from 3 to 9 months, but fathers’ ratings correlated over time, indicating individual-order stability. In a First-Difference Regression Model, increases in paternal involvement (play and primary caregiving) and infant cooperative behavior from 3 to 9 months predicted higher paternal sensitivity. Conclusions. Evidence for both group-level discontinuity and individual-order stability in fathers’ sensitivity and involvement was found at 3 to 9 months postpartum. Increases in paternal play and primary caregiving, along with cooperative infant behavior, predicted higher paternal sensitivity at 9 months, identifying modifiable targets for early support.engPsychologyFather involvementFather-infant interactionSensitivityStabilityPortugaljournal article10.1080/15295192.2025.2611322