How many states participate in proficiency testing?

Most parents send their children to either a public or private institution. According to government data, one-tenth of students are enrolled in private schools. Approximately 85% of students enter the public schools, largely because they are "free" (tax burdens by school districts vary from area to area). Most students attend school for around eight hours per day, and usually anywhere from 175 to 185 days per year. Most schools have a summer break period for about two and half months from June through August. This break is much longer than in many other nations. Originally, "summer vacation", as it is colloquially called, allowed students to participate in the harvest period during the summer. However, this is now relatively unnecessary and remains largely by tradition; it also has immense popular support.