The current study examined the validity of classroom-based English assessment in the elementary school context using a validity analysis framework, which includes cognitive, instructional, and inferential validity components. As a case study, it evaluated two unit achievement tests administered to 142 6th grade students. Three types of data (i.e., the curricular learning goals, instructional contents covered for the two units, and two unit achievement tests and scores) were collected and analyzed for the classroom-based assessment validity argument. Results revealed that the two tests were relevant to the curriculum and instruction; however, there was a lack of correspondence between the two tests and the curriculum (cognitive validity); moreover, the instructional contents were not sufficiently covered with representative test items (instructional validity). While the test items functioned as expected, students showed a wide range of achievement, which was not expected in the achievement test context (inferential validity). The findings suggest implications for the development and use of classroom-based assessment for young language learners.