The study collected information on the students' teachers and homes. Not surprisingly, the highest-scoring students had well-educated parents or came from homes containing study aids such as computers, dictionaries or even such elemental facilities as desks. The study also shows that boys generally did better than girls in science, but there was little difference between them in math. Boys scored better than girls in physics and chemistry. There were no sex differences in the life and environmental sciences. In addition to being tested, students in the project were asked how proficient they thought that they were in math and science. Students in some countries, such as Columbia and Kuwait, had an overly optimistic view of their skills. Meanwhile, some of the best students from Japan and Korea for example were needlessly pessimistic even though they did far better in math than almost all of other students.