The Pea Ridge School District violated the Americans with Disabilities Act in 2013 by excluding some students until they were tested for the human immunodeficiency virus, according to a letter from the U.S. Department of Justice. The district removed three students, all foster children, from its schools on the basis of documents it had received about the HIV status of a family member of those students, according to the letter dated Dec. 13 from Rebecca Bond, chief of the disability rights section of the department’s civil-rights division.