This naturalistic study assessed processes and outcomes in 8-week prevention-focused, school-based, girls' groups. Group processes were assessed at treatment sessions one, four, and eight via a round-robin method of data collection, and treatment outcome was measured with a pre-post treatment design. Changes in process and outcomes were calculated using residual gain scores. The first hypothesis was that a gains or losses of affiliation in the groups would be related to participants' social-interpersonal growth. The second hypothesis posited that increased positive feelings from the group towards the individual would be more predictive of positive treatment outcome than increased positive feelings from the individual towards the group. Exploratory analyses investigated (a) associations between subcategories of process and subcategories of outcome; (b) the relationship between affiliative processes at specific sessions and treatment outcome; and (c) charted trends of treatment process over time. Findings did not support the primary or secondary hypotheses. Exploratory analyses revealed that increased affiliation from other members resulted in increased social-esteem in group members. Also, higher initial levels of affiliation, and greater degrees of affiliation over time, distinguished the high- from the low-outcome groups. Future interventions should include increasing interpersonal connections at the onset of treatment in order to benefit those group members who are the least affiliated. Further process-outcome research is also recommended.