This paper investigates the magnitude of difference of academic achievement scores by language of instruction of prior education and the magnitude of interaction between language of instruction of prior education and students’ preferred learning trait on academic performance of a group of international students in two teaching and learning practices. The magnitude of difference and magnitude of interaction were determined by using Cohen’s d with Hedges g correction. Coe’s spread sheet was used for the analysis. The study showed that the magnitude of difference of academic achievement score was found to be very small on Traditional method of Teaching and Learning (TTL) and small on Problem-Based method of Learning (PBL). However, the magnitude of interaction between language of instruction of prior education and learning traits varied from very small to large. It is a challenging task to accommodate international students from different language background and optimize the whole learning process in an English speaking teaching and learning environment.