The study aims to analyze student responses to chemistry constructed response items to obtain detailed information on science NAEA (National Assessment of Educational Achievement) in South Korea and to draw suggestions for enhancing curriculum, teaching, and learning. For this purpose, we analyzed 7444 answers that could be generalized as 1.29% of the 9th grade students by the two-stage stratified cluster sampling method. The types of answers to constructed item were classified, and the response rate distribution curve according to the achievement score for each achievement level was drawn and analyzed. In this way, analyzing the descriptive answers is an advantage of the constructed response items; that is, students' responses vary widely, and they can systematically analyze the various types of misconceptions they have. As a result, students at the basic level tended to have misconceptions about the quantity of thermal energy, whereas students above proficient level had misconceptions about thermal equilibrium. Therefore, both the understanding and misconceptions of students differed according to achievement levels, so customized teaching and learning based on achievement levels should be developed. And the implications for curricula and improvement of teachers' expertise in assessment of constructed items are suggested.