(2007). Changes in Instructional Hours in Four Subjects by Public School Teachers of Grades 1 Through 4. U.S. Department of Education.
توثيق أسلوب شيكاغو (الطبعة السابعة عشر)Changes in Instructional Hours in Four Subjects by Public School Teachers of Grades 1 Through 4. U.S. Department of Education, 2007.
توثيق جمعية اللغة المعاصرة MLA (الإصدار التاسع)Changes in Instructional Hours in Four Subjects by Public School Teachers of Grades 1 Through 4. U.S. Department of Education, 2007.
تحذير: قد لا تكون هذه الاستشهادات دائما دقيقة بنسبة 100%.