5Judith Sowder. Estimation and Number Sense [J]. Handbook of Research on Mathematics Teaching and Learning, 1992, (4): 371-389.
6Robert Rey, Barbara Rey, Der Ching Yang. Assessing Number Sense of Student in Australia, Sweden, and the United States [J]. School Science and Mathematics, 1999, 99(2): 61-70.
7Der Ching Yang. Teaching and Learning Number Sense [J]. School Science and Mathematics, 2002, 102(4): 152-157.
8NCTM.Principles and Standards for School Mathematics.www.nctm.org,2000.
