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Special Agents of Δ Academy

Thursday 12:15 - 1:15 Session: S30 PreK - 2nd Level Carolina A Room

Building Blocks for Subtraction Success

Teachers who are still using rhymes and tricks to teach children the meaning of

regrouping in subtraction are hindering a new generation of mathematicians who

need to be taught the “why” behind subtraction. Too often, our students don’t
understand why they are crossing out numbers and writing other numbers above

them. Two SC Standards that frequently get overlooked in 1st and 2nd grade teach

the foundation for subtraction with regrouping. These standards teach students to

think flexibly about numbers by giving them multiple experiences in decomposing

numbers in multiple ways. Instead of always looking at 34 as 3 tens and 4 ones, the
standard 1.NSBT.2(c) says students should be able to think about 34 as 2 tens and

14 ones or 1 ten and 24 ones or 34 ones. In 2nd grade, 2.NSBT.1(c) says students

should be able to decompose 3 digit numbers in multiple ways. So, 158 can be 1

hundred, 5 tens, 8 ones or it can be 1 hundred, 4 tens, and 18 ones etc...Helping

students become confident in flexibly decomposing numbers by giving them
concrete experiences with manipulatives is the first step in laying the important

foundation that will build their knowledge of how numbers work. Transitioning this

thinking from the concrete to the representational and then to the abstract (CRA) is

critical in building the understanding students need to become fluent in subtraction

with regrouping, a skill that will be used in mathematics throughout life. This session
will give attendees background around these important standards. Hands-on

activities will be introduced that can be taken back and implemented immediately to

build student knowledge that will help them think flexibly about numbers, increasing

their ability to be successful problem solvers.

Lisa Ross, Heather Price

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