The researchers aimed to study the current and desirable conditions of cooperation professional development supervision practices in private schools in Thailand using needs assessment. A total of 165 respondents out of 894 private school directors, heads of department, and teachers who are working in private schools located in the northeastern region encompassing six provinces, namely UdonThani, SakonNakhon, KhonKaen, Chaiyaphum, and Sisaket provinces under the jurisdiction of the Private Education Commission were selected using a multistage sampling technique. These 165 respondents responded to a five-rating scale questionnaire. Besides, the researchers also employed documentary reviews as a research strategy for understanding and analyzing empirical realities through the review of 20 previous studies and public documents, collation, comparison, and understanding of different types of documentary sources referring to forms of cooperative professional development supervision practices of private schools, through a systematic and organized approach. Data were analyzed using descriptive statistics such as mean scores, standard deviation, and priority needs index modified and also the inferential statistic that was paired t-test. The research results from documentary reviews revealed that there are six scopes of cooperative professional development supervision practices in private schools derived from the 20 reviewed documents. These six scopes of cooperative professional development supervision were educational curriculum development, promoting students’ reading and writing skills, active learning management, using digital technology in learning management, upgrading achievement, and quality assurance. The quantitative results from needs assessments indicated that the overall current condition of cooperative professional development supervision practices in private schools was found at a moderate level ( = 3.19) while the desirable condition was at the highest level (( = 4.56, SD = 0.31), respectively. Finally, the needs assessment findings demonstrated that the highest priority was the scope of active learning management (PNImodified= 0.48), followed by the scope of quality assurance (PNImodified= 0.44), the scope of upgrading achievement (PNImodified= 0.43), the scope of promoting students’ reading and writing skills (PNImodified= 0.42), and scope of educational curriculum development (PNImodified= 0.41). The lowest priority index of needs was the scope of using digital technology in learning management (PNImodified= 0.40). In conclusion, the results contribute significantly to knowledge concerning needs assessments which would be the reference for private school directors, heads of departments, and teachers to understand how to promote cooperative professional development supervision practices

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