In classes for adults, a day of attendance is 180 minutes of attendance but no student shall be credited with more than 15 clock hours of attendance per school week, proportionately reduced for those school weeks having weekday holidays on which classes are not held unless he or she is enrolled in a class in elementary subjects, a class for which high school credit is given, a class in English for foreigners, a class in citizenship, or a class in a trade or industrial subject as trade or industrial subject is defined by the State Board of Education for grades 7 to 12, inclusive.