This study aims to explore how to develop the diagnostic assessment of basic competency(DABC) in middle school Korean language learning, specially focused on the achievement standards for assessment and frame of developing test items. DABC should be designed to be based on the current national curriculum. If DABC is developed based on the 7th National Curriculum Korean language, it is most desirable to focus on the 'basic' level of the contents, considering the characteristics of differentiated curriculum. And the frame of test items is able to be organized as the two dimensions of assessment, contents and behaviors, the former is constituted by 'listening and speaking', 'reading', 'writing', 'grammar', 'literature', and the latter is constituted by 'understanding', 'applying', 'critiquing'. Considering the characteristics of DABC, 'reading' and 'understanding' should be given more weight. DABC is criterion-referenced evaluation and the result are reported to the students, teachers, schools with two levels such as Basic and Below-Basic. The cut-off score dividing the levels was determined by bookmark method.