In order to obtain the understanding and difference of general students and disadvantaged students (the socio-economically disadvantaged group, low achievement group, new immigrant children) in their mathematic learning interest and confidence, this research established ”The scale for lower grade students in their mathematic learning interest and confidence”. Complementary instruction of mathematics was used by disadvantaged students. Then the scale was used in the post-test. The result of research was presented as follow: (1) The scale showed a good reliability and validity after the analysis of experts and pre-tests; (2) Complementary instruction of mathematics could enhance the mathematics learning interest and confidence; (3) The socio-economically disadvantaged group and new immigrant children in their mathematic learning interest and confidence and achievement of mathematics didn't show weakness. Finally, based on the findings of the research, some suggestions were given for reference.