The purpose of this study was to develop a mechanical critical thinking scale for high school students. A stratified random sampling method was used to establish the norms. After pre-tests and item analysis, the scale was determined to have five subtest sections (i.e., recognition of assumptions, induction, deduction, interpretation, and evaluation of arguments) consisting of 25 items. In addition, using 1,954 high school students as participants, this study established a norm and investigated the differences among genders and ages. The results showed that male students had better mechanical critical thinking skills than did female students in terms of induction aptitude, while female students were better in evaluation aptitude. In addition, the mechanical critical thinking performance of 12th-grade students was superior to that of 10th- and 11th-grade students.