The purposes of this research were: (1) to study the requirements for the competency development of social studies pre-service teachers in the Chiangmai Education Sandbox Area; (2) to develop a manual for the competency development of social studies pre-service teachers in the Chiangmai Education Sandbox Area; and (3) to study the results of the Area-Based Approach to the transversal competency development of social studies pre-service teachers. The study was descriptive and included 64 participants in total: (1) 33 school administrators, supervisors, and teachers; and (2) 31 social studies pre-service teachers. A volunteer sampling method was used. The research instruments included: (1) a non-structured interview; (2) an assessment of the manual; and (3) an assessment of competency. In the data analysis, a content analysis was carried out and presented in description, and the quantitative data were analyzed to find means and standard deviation. The results of the study revealed the following: (1) the 4 main competencies schools require of the social studies pre-service teachers are: (1) content knowledge; (2) learning management; (3) engagement strategies; and (4) professional development; (2) a manual for the area-based approach was developed, consisting of 4 learning units in 4 steps referred to as the "AAAR Area-Based Approach". It was judged to be very appropriate and effective; and (3) the results of the assessment of the perception of the social studies pre-services teachers regarding the area-based competencies in the Chiangmai Education Sandbox Area was at the 'good' level.