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In first grade, students build on what they've learned about making 10 and teen numbers in kindergarten and expand that thinking to solidify their understanding of place value. Students learn to compose and decompose teen numbers with increased understanding to help add and subtract within 100. This should be done at the abstract level, using numbers and math symbols. At this stage, students should be able to use representational models of tens and ones as their understanding of place value strengthens. The counting sequence is extended to 120 and students begin to compare 2-digit numbers using the greater than (>) and less than (<) signs. As this concept is introduced, students should have plenty of access to a variety of math tools that will guide their understanding.
Common Core State Standards
Common Core State Standards
Extend the counting sequence.
Count to 120, starting at any number less than 120. In this range, read and write numerals and represent a number of objects with a written numeral.
Understand place value.
Understand that the two digits of a two-digit number represent amounts of tens and ones. Understand the following as special cases:
10 can be thought of as a bundle of ten ones — called a "ten."
The numbers from 11 to 19 are composed of a ten and one, two, three, four, five, six, seven, eight, or nine ones.
The numbers 10, 20, 30, 40, 50, 60, 70, 80, 90 refer to one, two, three, four, five, six, seven, eight, or nine tens (and 0 ones).
Compare two two-digit numbers based on meanings of the tens and ones digits, recording the results of comparisons with the symbols >, =, and <.
Use place value understanding and properties of operations to add and subtract.
Add within 100, including adding a two-digit number and a one-digit number, and adding a two-digit number and a multiple of 10, using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction; relate the strategy to a written method and explain the reasoning used. Understand that in adding two-digit numbers, one adds tens and tens, ones and ones; and sometimes it is necessary to compose a ten.
Given a two-digit number, mentally find 10 more or 10 less than the number, without having to count; explain the reasoning used.
Subtract multiples of 10 in the range 10-90 from multiples of 10 in the range 10-90 (positive or zero differences), using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction; relate the strategy to a written method and explain the reasoning used.
This video demonstrates how 2-digit numbers are composed and decomposed.
Comparing numbers using greater than and less than representations and mathematical symbols are introduced in this video.
Number chips (base ten blocks can be substituted) are used to model 2-digit addition with multiples of ten.
Concrete Level: Using math manipulative to compare 2-digit numbers
The concept of comparing 2-digit numbers builds on students' understanding of place value. As this concept is introduced to students, they should be given plenty of time and practice comparing numbers using a variety of math tools.
Representational Level: Adding and subtracting within 100
Representational Level: Adding and subtracting within 100
Students have experience with place value and composing/decomposing numbers within 100. They will be expected to use representations of tens and ones to solve basic computation.
Abstract Level: Decomposing teen numbers and comparing using greater than and less than symbols
Composing and decomposing teen numbers has been introduced to students in kindergarten. In grade 1, they will be building on that skill and growing their understanding of place value and the value of digits in the tens and one's places. They should be exposed and expected to use the abstract form of decomposing teen numbers. Towards the end of the school year, students are exposed to the greater than (>) and less than(<) signs.
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