The school term shall not be less than (1) one thousand thirty-two instructional hours for elementary grades and (2) one thousand eighty instructional hours for high school grades in any public school district or private, denominational, or parochial school. If any district which receives twenty percent or more of its total receipts for general fund purposes from federal sources fails to actually receive receipts anticipated at the time of the adoption of the school budget from taxes, state funds, federal funds, tuition, or other sources, the school board or board of education of such district may, at any time during the school year, elect to close all or part of its schools.