Open schools (also known as informal schools or open classrooms) operate under the central theory that children want to learn and will do so naturally if left to their own initiative. The open classroom is marked by learning areas, often without walls. Students are free to move from area to area, learn at their own pace and enjoy unstructured periods of study. Developed in Britain, this school model becomes popular in American elementary schools in the 1960s. But by the mid-1970s, open classrooms will be criticized by those advocating a return to a more traditional emphasis on reading and writing fundamentals and more structured classrooms.