Objective To determine whether a parent–youth teamwork intervention improved medication adherence and related outcomes among youth with asthma. Methods We used a randomized clinical trial with 48 youth (aged 9–15 years) assigned to 1 of 3 groups: Teamwork Intervention (TI), Asthma Education (AE), or Standard Care (SC). Treatment occurred across 2 months, with a 3-month follow-up assessment. Adherence to inhaled corticosteroids was assessed via the MDILog-II. Parent–adolescent conflict, asthma functional severity, and spirometry assessments were obtained pre-treatment, post-treatment, and on follow-up. Mixed linear model analysis was used to evaluate group and time effects for outcome measures. Results TI group had significantly higher adherence and lower functional severity scores than AE or SC conditions, and lower parent-reported conflict and a trend for higher spirometry values compared with the SC group. Conclusions Results suggest support for the efficacy of TI for improving medication adherence as youth acquire more responsibility for their asthma management.