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B. Choosing Instructional Strategies
Consider the following guidelines for teaching addition and subtraction:
•
Use "subtract" or "minus," but not "take away," so as not to reinforce a narrow, incomplete
definition of subtraction.
•
Interchange "is the same as" with "equal" frequently to reinforce the meaning of "equal."
•
Teach frequently in a problem-solving context. Research shows that by solving problems
using addition and subtraction, students create personal strategies for computing and develop
understanding about the relationship between the operations and their properties (NCTM
2000, p. 153). Overly simple problems make it easy for some students to develop strategies
such as identifying two large numbers in a problem means that you add, whereas a large and
a small number in a problem indicate subtraction.
•
Provide time for students to create personal strategies to solve the problem and share these
strategies with members of their groups or with the entire class.
•
Choose problems that relate to the student's own lives. Contextual problems might derive
from recent classroom experiences, including literature sharing, a field trip, or learning in
other subject areas such as art or social studies.
•
Provide a variety of problems representing the different addition and subtraction situations
with varying degrees of difficulty to differentiate instruction.
•
Work with the whole group initially and have the students paraphrase the problem to enhance
understanding and to recognize which numbers in a problem refer to a part or to a whole.
•
Provide a variety of manipulatives, including base ten blocks and others that can be grouped
in tens and ones, such as tiles, pennies, stir sticks, straws, ice cream sticks, Unifix cubes,
multilinking cubes or beans for students to use as needed.
•
Guide the discussion about the operations of addition and subtraction by asking questions to
encourage thinking about number relationships, the connections between addition and
subtraction and their personal strategies. Such questions could include:
1.
When we add two numbers, is the sum usually bigger or smaller than either of the
numbers? We have to be careful not to say "always bigger," since when students add
negative numbers eventually, this is not so. Also, when we add zero, the number stays the
same.
2.
When we subtract two numbers, is the difference usually less than or more than the
number we subtracted from?
3.
Does the difference change if we subtract a subtrahend one larger than the last from a
minuend that is one larger than the last? What about if we decrease both numbers in the
subtraction problem by one? What if we were to increase or decrease both numbers in the
problem by 2? What if we increase the minuend by 1 and the subtrahend is decreased by 1?
4.
Can we break numbers up in ways that make it easier for us to add or subtract the parts in
order to arrive at the answer mentally and efficiently?
•
Challenge the students to solve the problem another way, do a similar problem without
models or clarify the explanation of their personal strategies.
•
Have the students evaluate their personal strategies as well as those of their classmates to
decide which strategy works best for them and why.
•
Limit the number of story problems that students are solving a day to one or two and leave
half a page where each solution can be shown and explained.
www.LearnAlberta.ca
Grade 2, Number (SO 8, 9)
© 2008 Alberta Education
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