Objectives This study is expected to face many difficulties in operating guidance that guarantees the minimum level of achievement following the introduction of the high school credit system, so it seeks to listen to the opin-ions of teachers and experts, focusing on the case of the Gangwon Special Self-Governing Provincial Office of Education, and propose support measures to prevent failure to reach the minimum level of achievement. Methods To this end, in-depth interviews (2023. 4. - 2023. 6.) was carried out. The questions of the in-depth in-terview consisted of the suitability of the purpose of preventive guidance to guarantee the minimum level of ach-ievement, differences in teachers' perceptions and practices, the actual state of operation and impediments, and the performance of suitable operation plans and policies. Results Through interview analysis on the cases of the Gangwon-do Office of Education’s guidance for guaran-teeing the minimum achievement level of the high school credit system, the results were analyzed from five as-pects: (1) perception, (2) practice, (3) class, (4) evaluation, and (5) environment. Opinions were understood. In ad-dition, implications were drawn by analyzing the current status of guidance for guaranteeing the minimum ach-ievement level of the high school credit system of other city and provincial offices of education, and cases of pre-vention and supplementary guidance for guaranteeing the minimum achievement level for research and prepara-tion schools at the Gangwon Metropolitan Autonomous Office of Education. Conclusions Firstly, as reviewed in the 2022 achievement evaluation results of high schools (107 schools) of the Gangwon-do Office of Education, it was confirmed that more than 40% of the students had academic achieve-ment E. Secondly, as a result of analyzing the operational tasks of research schools and preparatory schools of other city/provincial offices of education and the Gangwon Metropolitan Autonomous Provincial Office of Education and identifying their characteristics, the main factors were methods of selecting low-achieving students, af-ter-school operation of non-attainment prevention guidance, and emotional support programs. Thirdly, measures to improve and support classes and assessments were proposed to have the subject competencies presented in the 2015 revised curriculum based on everyday life and familiar subjects, rather than just achieving the quantita-tive goal of the subject to reach the minimum achievement level.