Schools in the United States are divided into elementary, junior high and senior high schools, depending on the age of the child.  At the preparatory stage (where enrollment is not voluntary), children aged five to six years old are prepared for school at kindergartens: they are taught to read, write and read. In primary school, most of the lessons are taught by one teacher. The main attention is paid to social skills, behavior, physical exercise and creativity.  In junior high school, children study the compulsory subjects at a deeper level and are assigned a significant amount of homework. In senior high school, students choose the subjects in which they will take tests for admission to a university. Public schools are free for children who are resident in the US. More than 90% of American children go to public schools.