ObjectiveThis longitudinal study involved youths in residential care due to previous adverse experiences and their educators, aiming to investigate the role of youths and educators' attachment, educators' psychopathology, and the quality of youth–educator relationship on change scores of youths' symptoms and youth–educator relationship security over 6 months.MethodParticipants were 36 institutionalized youths (Mage = 16.50 ± 2.13) and their 25 main educators (Mage = 38.48 ± 5.75), assessed at baseline (T1) and 6 months later (T2). Youths were assessed in total, internalizing and externalizing problems via a multi‐informant approach, and educators in psychopathology levels. Attachment representations of youths and educators were assessed through validated attachment interviews (Friends and Family Interview and Adult Attachment Interview), and both separately rated the youth–educator relationship.Results(1) Most cases remain stable over 6 months. (2) Educator narrative coherence and the quality of youth–educator relationship at baseline were correlated but not predictive of change in youths' symptoms. (3) Youths' higher attachment disorganization at baseline was the unique predictor of 14% variance of positive change in the youth–educator relationship security perceived by the youth. (4) Youth attachment avoidance uniquely predicted 37% of positive change variance in the youth–educator relationship security perceived by educators.ConclusionIn conclusion, attachment‐based assessment of youths and educators can inform intervention to foster youth improvement.