Purpose
This study aimed to understand the characteristics of adult learning by examining the instructional process and strategies adopted by instructors who taught nonformal curricula (NCs) at community colleges. This study also observed the learning achievement and results of transformative learning among the students who studied these courses. According to the assessment on the NC instruction approaches employed by instructors and the learning achievement of students engaging in NCs, this study proposed a theoretical framework on verifying the learning achievement associated with nonformal learning and provided relevant suggestions for future development.

Design/methodology/approach
By employing the grounded theory method for qualitative research, a total of 17 people, namely 5 instructors and 12 students, were interviewed to explore their personal experiences.

Findings
This study held that NC instructional methods for instructors and learning assessment for students should be designed according to the requirements of adult-learning assessment. Transformative learning occurred among adult students at community colleges, who connected with their intrinsic characters. Regarding the instructional quality of NCs at community colleges, the learning achievement of adult students who studied in NCs was focused on practice and experiential learning; thus, NC accreditation (NCA) helped increase NC quality through synergy, even though it was not required. In particular, promotions and complementary measures implemented by community colleges affected the quality of NCA.

Originality/Value
This study examined the NCA that has been implemented in Taiwan from the perspective of adult learning by conducting empirical research. Instructors and students from community colleges in Taiwan were interviewed, and their instructional strategies and learning achievement were explored. The findings of this study can be a reference for the development of relevant policies and studies in the future.