Background:
The purpose of this study was to develop a mechanical critical thinking scale (named the “Mechanical Critical Thinking Scale”) for high school students.

Material and methods:
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 consisting of 25 question items.

Results:
Difficulty indexes of all items were between 0.37 and 0.90 with an average of 0.61, and the discrimination indexes were between 0.17 and 0.68 with an average of 0.45. Reliability and validity analyses showed that the mechanical critical thinking scale developed in this study had a moderate difficulty and satisfactory reliability and validity. In addition, using 1,954 high school students (766 10th-grade students, 459 11th-grade students, and 729 12th-grade students) as participants, this study established a norm and investigated the differences among genders and ages.

Conclusions:
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 mechanism critical thinking performance of 12th-grade students was superior to that of 10th- and 11th-grade students.