This paper examines how various intervention arrangements can be applied to study the effectiveness of clinician attitudes in relation to offenders with intellectual disabilities (ID) in a forensic context. The research assesses the effect of training and knowledge-based interventions on the clinician attitude and treatment outcome using a mixed-method approach. The study proves that the Combined Approach (Full), which combines training and knowledge-based factors, significantly enhanced the most important metrics such as Attitude Change, Knowledge of ID, Level of Empathy, and Confidence in Treatment. In particular, the Attitude Change increased from 2.5 to 4.2, representing a 68% improvement, and the Knowledge of ID increased from 3.1 to 4.5, representing a 45.16% improvement. The Empathy Level had improved by 46.67, and Confidence in Treatment had increased by 34.38. These changes led to an increase in the Treatment Success Rate from 60% to 80%. The Knowledge-Based setting recorded a success rate of 75 per cent, whereas the Training Only group recorded the least improvements with a 70 percent success rate. The findings of the study highlight the immense importance of integrating the principles of Motivational Interviewing and Good Lives Model in the improvement of clinician attitudes and effectiveness of treatment. The research proposes that the effectiveness of the rehabilitation process may be enhanced as a result of the advancement of the attitude of the clinicians toward the offenders with ID, which will result in the reduction of the recidivism rates and the subsequent successful reintegration into the social environment. Future researchers ought to determine the long-term viability of these interventions and how effective in different criminal justice contexts.