Monitoring/controlling behaviours can be present in the early stages of an abusive relationship. Because of the need for evidence-based interventions grounded on behavioural models that identify the determinants of abusive behaviours, we applied the formative research of the reasoned action approach to: (1) conduct an elicitation study on the behavioural and normative beliefs that explain why boys use mobile phones to monitor their girlfriends and why these accept it, (2) analyse the items designed to assess the different constructs in the model and (3) carry out a preliminary exploration of the relationship between constructs. The sample was composed of 119 adolescent girls and boys between 14 and 18 years of age. Boys and girls seem to hold complementary beliefs that could produce a feedback loop that maintains the abusive behaviour. Parents are a protective factor against the behaviour whereas peers are not. Results on the item analysis and reliability of the scales were good. Intention seems an important predictor of the performance (51%) and acceptance (60%) of the behaviour and attitudes and perceived social norms of the intention (boys: 67%; girls: 65%), which suggests the appropriateness of the model for the prediction of the behaviour.