Tables 4, 5, and 6 showed the accuracy of each item for the inner-school achievement test, the descriptive data analysis, and the results of the t-test. It was indicated statistically that the subjects using the combinatorial approach instruction scored significantly higher than those taught using the traditional approach on multiplicative identities content achievement
(p < 0.001) (total items). Especially, the accuracy of the unfamiliar problems revealed that the experimental group students performed significantly better than control group students. Because nobody in the control class could get the correct answer for the ninth item “〖(a+b)〗^3= ?”, while the accuracy of the experimental class was 43.8%, the first author interviewed the students.