All reservation and nonreservation boarding schools with an average attendance in any year of less than forty-five and eighty pupils, respectively, shall be discontinued on or before the beginning of the ensuing fiscal year. The pupils in schools so discontinued shall be transferred first, if possible, to Indian day schools or State public schools; second, to adjacent reservation or nonreservation boarding schools, to the limit of the capacity of said schools: Provided, That all day schools with an average attendance in any year of less than eight shall be discontinued on or before the beginning of the ensuing fiscal year: Provided further, That all moneys appropriated for any school discontinued pursuant to this section or for other cause shall be returned immediately to the Treasury of the United States.