The proportion of full-time teachers is positively associated with students' science performance only in Bulgaria, Colombia, Japan, Malta, Peru, Chinese Taipei, andTrinidad andTobago, in Luxembourg, Qatar and Switzerland, the association is negative. Just as practitioners in any other profession, teachers need to keep up-to-date with advances in their field. They are often expected to learn about new ways of teaching, discoveries in their field of expertise, new theories about how children learn, curricular changes or innovative tools for the classroom.