1. Liping Ma, Knowing and Teaching Elementary Mathematics, (Mahwah, New Jersey: Lawrence Erlbaum Associates, Publishers, 1999)p. 22-23
2. Marilyn Burns,
About Teaching Mathematics: A K-8 Resource Publications,
(White Plains, New York: Math Solutions, 1992) p. 18
3. Leonard M. Kennedy, and Steve Tipps,
Guiding Children’s Learning of Mathematics,
(Belmont, California: Wadsworth Publishing Company, 1991) p.123
4. Burns, p. 19
5. Ma, p. 17-19
6. Ma, p. 15-18
