Objective: Family-based treatment for anorexia nervosa (FBT) has demonstrated efficacy in the treatment of adolescents with anorexia nervosa (AN) in a number of randomized control trials (RCT). The aim of the current research was to determine whether adherence to the key components of the model as outlined in the treatment manual predict weight gain or dropout. Method: The 59 participants were under 19 years and had AN for less than 3 years. Five core treatment objectives and working alliance were measured across 20 sessions of FBT. Results: The core objectives of parents taking control, being united, not criticizing the patient and externalizing the illness predicted greater weight gain. Sibling support did not predict weight gain. The relationship between therapeutic alliance and weight gain was positive for mothers but negative for fathers. Dropout was predicted by low control and poor maternal-therapeutic alliance. Discussion: The results of this study lend further support for the efficacy of the FBT, demonstrating that the principles guiding clinical practice are those which lead to weight gain. The finding that parental control is the central predictor of change can also support the development of augmentations to the model.