Every child between the minimum and maximum ages established for school attendance by the board of education, except a child between fourteen and sixteen who meets the requirements for the completion of the sixth grade of the public school as established by said board and who holds a permit for employment in private domestic service or service on a farm, under section eighty-six of chapter one hundred and forty-nine, and is regularly employed thereunder for at least six hours per day, or a child between fourteen and sixteen who meets said requirements and has the written permission of the superintendent of schools of the town where he resides to engage in non-wage-earning employment at home, or a child over fourteen who holds a permit for employment in a cooperating employment, as provided in said section eighty-six, shall, subject to section fifteen, attend a public day school in said town, or some other day school approved by the school committee, during the number of days required by the board of education in each school year, unless the child attends school in another town, for said number of days, under sections six to twelve, inclusive, or attends an experimental school project established under an experimental school plan, as provided in section one G of chapter fifteen, but such attendance shall not be required of a child whose physical or mental condition is such as to render attendance inexpedient or impracticable subject to the provisions of section three of chapter seventy-one B or of a child granted an employment permit by the superintendent of schools when such superintendent determines that the welfare of such child will be better served through the granting of such permit, or of a child who is being otherwise instructed in a manner approved in advance by the superintendent or the school committee.