In the United States, "junior high" -- also known as "middle school" -- immediately follows elementary (or "primary") school. Junior high boarding schools generally take students in the 6th, 7th and 8th grades. In general, a junior high boarding school will not include instruction above or below these grades; in some cases, such as for a preparatory school offering a junior option, boarding schools incorporate all secondary education, from 6th grade through 12th grade.
Many junior boarding schools are general purpose, and simply serve as places where students can be educated in an environment where they are surrounded by their peers at all times. Other boarding schools, however, have specific purposes or interests. They may be aimed at students for whom behavioral problems make ordinary schools inappropriate, for example. A boarding school may be intended for students with specific learning disabilities or other special needs for which instruction and expertise can be effectively concentrated in one academy.
Junior high boarding schools share most of the missions and practices of those schools serving older students. There are, however, some key differences: As expected, given the younger age of the students, preparation for college may be downplayed in favor of a focus solely on education, or on preparation for high school. Most military boarding schools, as well, are geared toward older students; if you're looking for a military school you may be hard pressed to find a junior high boarding school to fill this role.
Before committing to a boarding school, you should have a good understanding of your needs. Consider whether your child requires special instruction that can only be provided at a school targeted to similar students, or whether a general-purpose boarding school is appropriate. Carefully weigh all your options; the Junior Boarding School Association, a network of primary and intermediary boarding schools, suggests that you complete a tour of schools before making your decision. Examine your prospective schools carefully, and consider whether or not their mission statement matches your own beliefs and goals for your child.