The present study examined the relationship between dyadic interaction patterns and implicit theories of relationships (ITRs; deeply held beliefs about the nature of relationships) using a sample of N = 104 couples. We hypothesised that destiny beliefs would predict greater avoidance in conflict interactions, while growth beliefs would predict more constructive communication. Surprisingly, the results of the current study challenge the existing literature by indicating that neither destiny nor growth beliefs predict constructive communication or mutual avoidance for the couple. Further, while destiny beliefs were related to increased withdrawal in a demand-withdraw pattern, growth beliefs related to both demand and withdraw in a demand-withdraw pattern. These findings suggest that assessing the relationship between ITRs and communication patterns at the couple level introduces complexity that is underexplored in the current literature on implicit theories of relationships.

School engagement has been shown to be a strong predictor for school achievement. Previous studies have focused on the role of individual and contextual factors to explain school achievement, with few examining the role of siblings. This study used data of 451 adolescent sibling pairs from the Iowa Youth and Families Project to investigate the associations between school engagement and achievement in siblings by considering gender composition and birth order. Data were collected in families’ home and obtained for a target child in the 7th grade and for a sibling within 4 years of age. Average age of younger siblings (55% female) was 11.56 (SD = 1.27), while older siblings (49% female) had an average age of 13.92 (SD = 1.47). Using the two-member, four-group actor-partner interdependence model (APIM), results showed that older siblings’ engagement was positively related with younger siblings’ achievement in same-gender sibling pairs, but not in sibling pairs of opposite gender. Younger siblings’ engagement was independent of older siblings’ achievement regardless of siblings’ gender. Implications for parents and professionals suggest that support for older siblings could also benefit younger siblings in same gender pairs.