tThis study explores whether using the open approach instruction in teaching mathemat-ics has a positive effect for enhancing pre-service teachers’ fraction knowledge. The testconsisted of 32 items that were designed to examine pre-service teachers’ procedural andconceptual knowledge of fractions before and after receiving open approach instruction.The study was undertaken among students in four mathematics content and methodscourses for the Elementary School Education program in a mid-western public university.The findings show that most of the teachers achieved improved learning outcomes throughthe open approach instruction.