The purposes of this study were to investigate the practice of performance assessment in elementary mathematics classes especially focused on 4th grade. To achieve this, three research questions were posed as follow: First, What do they prepare for performance assessment? Second, What kinds of tests do they use in mathematics performance assessment? Third, What kinds of difficulties do they have for performance assessment and what should be changed for a successful performance assessment in mathematics? To Answer the research questions, three 4th grade classes were selected from three different elementary schools in seoul and three teachers were interviewed. From the data analysis, several conclusion were drawn. First, a plan for mathematics performance assessment was not set by the class teacher who are in charge of the class. The main reason was lack of time. Second, in most of the assessment, written tests were used and the items in the tests were skill-oriented. Third, teachers thought that performance assessment was needed in mathematics. But lack of their time, knowledge and competency, it is difficult to do performance assessment in mathematics.