The purpose of the current study is to explore the predictors of the Diploma Program scores in biology to resolve the dilemma regarding which international school curriculum is better to prepare students for the Diploma Program. A purposive sample of 135 high school students was drawn from a private international school in Turkey. Data was analyzed with a multiple regression approach. A statistically significant and relatively strong relationship was found between the Diploma Program scores in biology and the International General Certificate of Secondary Education science exam scores.