By using the data envelopment analysis method, the objective of this study is to examine the operational efficiency of Taiwanese private senior high school and vocational high school before and after implementing 12-year compulsory education. The empirical evidence demonstrates that only 4 of 19 sample schools are able to maintain their operational efficiency of maximum value to one. Additionally, on average, the operational efficiency of the sample schools was declining after implementing 12-year compulsory education. Such results imply that free tuition for private senior high and vocational school students narrow the gap in tuition between them. However, this also suggests that because of free tuition and proximity of the public schools, it results in higher enrollment in public schools. Yet, it adversely made private senior high school and vocational high school difficult to enroll students, hence, decreasing the operational efficiency of both private senior high school and vocational school.