This study explores the validity of school-based assessments when they serve to supplement scores on central tests in high-stakes examinations. The school-based continuous assessment (CA) marks are compared to the marks scored on the central written Bhutan Certificate of Secondary Education (BCSE) examination, to detailed teacher ratings of student competencies, and to student self-ratings. A survey was undertaken in 10 higher secondary schools, involving 26 English teachers and 365 graduates. Though results indicate moderate conformity among measurements within schools, results between schools indicate that schools with high average scores on the BCSE exam tend to score relatively low CA averages and vice versa. Compared to the CA marks for student performance in English listening and speaking skills, the detailed teacher ratings of students on the same skills correlate more strongly with the BCSE exam marks and the student self-ratings.