Exact prices change frequently, which is why only approximate ranges are listed.
$ - Under $5
$$ - Between $6 and $50
$$$ - Between $51 and $250
$$$$ - Over $250
Bassarear, T. (2011). Mathematics for elementary school teachers (5th ed.). Belmont, CA: Brooks/Cole.
Brown, C. N. (1979). Fractions on grid paper. The Arithmetic Teacher, 26, 8-10,
Cooper, R. (1994). Alternative math techniques instructional guide. Bryn Mawr, PA: Center for Alternative Learning.
Hall, W. D. (1981). Using arrays for teaching multiplication. The Arithmetic Teacher, 29, 20-21
Written by Bronwyn Lamond, Last Revision March 2018