This study is within the framework of the United Nations sustainable development goals related to equitable quality education. The total score on the 2015 Trends in International Mathematics and Science Study that indicated eighth-grade girls in Jordan significantly outperformed boys is hiding many details related to the quality of mathematics learning that reflect a gender gap. Data were analyzed using the Mantel-Haenszel differential item functioning analysis procedure to investigate test items that favored either boys or girls. The results showed that boys were more likely than girls to correctly answer the more difficult, unfamiliar, life-related mathematical problems. In contrast, girls were more likely than boys to correctly answer the familiar, less difficult, and not life-related problems. Some recommendations were suggested to diminish this gender gap that goes each way.