U.S. Dept. of Health, Education, and Welfare, Office of Education, National Center for Educational Research and Development; for sale by the Supt. of Docs., U.S. Govt. Print. Off.1969 [i. e. 1970]<FC23-30>
U.S. Dept. of Health, Education, and Welfare, Office of Education, National Center for Educational Research and Development : for sale by the Supt. of Docs., U.S. Govt. Print. Off.1970.<FC23-27>