ESTIMATING
RESEARCH FINDING:
Although students need to learn how to find exact answers to
arithmetic problems, good math students also learn the helpful
skill of estimating answers. This skill can be taught.
COMMENT:
Many people can tell almost immediately when a total seems right
or wrong. They may not realize it, but they are using a math
skill called estimating.
Estimating can also be valuable to children learning math.
When students can make good estimates of the answer to an arith-
metic problem, it shows they understand the problem. This skill
leads them to reject unreasonable answers and to know whether
they are "in the ballpark."
Research has identified three key steps used by good estimators;
these can be taught to all students:
. Good estimators begin by altering numbers to more man-
ageable forms--by rounding, for example.
. They change parts of a problem into forms they can handle
more easily. In a problem with several steps, they may rearrange
the steps to make estimation easier.
. They also adjust two numbers at a time when making their
estimates. Rounding one number higher and one number lower is an
example of this technique.
Before students can become good at estimating, they need to have
quick, accurate recall of basic facts. They also need a good
grasp of the place value system (ones, tens, hundreds, etc.).
Estimating is a practical skill; for example, it comes in very
handy when shopping. It can also help students in many areas of
mathematics and science that they will study in the future.
Bestgen, B., et al. (l980). "Effectiveness of Systematic In-
struction on Attitudes and Computational Estimation Skills of
Preservice Elementary Teachers." Journal for Research in Mathe-
matics Education, Vol. 11, pp. 124-l36.
Reed, S. K. (l984). "Estimating Answers to Algebra Word Prob-
lems." Journal of Experimental Psychology: Learning, Memory and
Cognition, Vol. l0, pp. 778-790.
Reys, R., et al. (l982). "Processes Used by Good Computational
Estimators." Journal for Research in Mathematics Education, Vol.
13, pp. l83-20l.
Schoen, H. L., et al. (l98l). "Instruction in Estimating Solu-
tions of Whole Number Computations." Journal for Research in
Mathematics Education, Vol. 12, pp. 165-178.
Trafton, P. R. (l978). "Estimation and Mental Arithmetic: Im-
portant Components of Computation." In Developing Computational
Skills, l978 Yearbook. Reston, VA: National Council of Teachers
of Mathematics.