Grade 2 · Math · Unit

Adding and Subtracting Within 100

9 lessonsabout 5 weeks

The unit ends with three more days: a review day, the unit check, and a day to act on what the check showed.

Unit 3 of 9 in the Grade 2 Math Scope and Sequence

What's included in this unit

9 lessons in teaching order, each with its objective and a teacher note
36 practice pages to print, with an easier and a harder page where available
5 classroom tools for the projector
4 activities and pages that children do on a screen
8 check-up pages to collect

The whole unit in one file

Print every page of the unit at once, with the teacher guide first. The guide has one page per lesson: the objective, what to hand out, and the teacher note.

Teacher guide only (PDF)

The unit file, the teacher guide, and saved pages are included with the Teacher plan.

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Lessons

Lesson 1

A number line that does not start at zero

Children read the number an arrow points to on a number line that starts at 40 or at 60 and has only some of its numbers printed.

StandardCommon Core 2.MD.B.6Measurement and Data

3 class days

Day 1Teach: The Landing Strip · Practice on paper (Core page)
Day 2Practice and check: Practice on paper (Easier page, Harder page) · Practice on screen · Check-up page
Day 3Reteach and extend: Act on the check-up pages: reteach the children who are not there yet, with the tool and a new page from the maker; the others take a harder page.

Warm up and teach

Open The Landing Strip on the projector.

Practice on paper

Where on the Number Line? 40 to 60
Core page Easier page Harder page
Where on the Number Line? 60 to 100
Core page Easier page Harder page

Lesson 2

Jumps on the hundreds chart

Children follow arrows on a hundreds chart, adding or taking away tens and ones, and write the number where they land.

StandardCommon Core 2.NBT.B.5Number and Operations in Base Ten
ReviewsCommon Core 1.NBT.C.5Number and Operations in Base Ten
Prepares forCommon Core 2.NBT.B.8Number and Operations in Base Ten

3 class days

Day 1Teach: The Number Hotel · Practice on paper (Core page)
Day 2Practice and check: Practice on paper (Easier page, Harder page) · Practice on screen · Check-up page
Day 3Reteach and extend: Act on the check-up pages: reteach the children who are not there yet, with the tool and a new page from the maker; the others take a harder page.

Warm up and teach

Open The Number Hotel on the projector.

Practice on paper

Jump Puzzles: Follow the Arrows
Core page Easier page Harder page
Mystery Number: Two Arrows, One Square
Core page Easier page Harder page

Practice on screen

Ten More, Ten Less — Mental Math With Two-Digit Numbers

Check-up page

One more page of Jump Puzzles: Follow the Arrows to collect at the end of the lesson.

Make more

Make more pages like this with the Number Charts and Number Sequences maker.

Lesson 3

Jumps on an open number line

Children add and subtract two-digit numbers within 100 on an open number line: they mark the starting number, draw their jumps, and write the answer.

StandardCommon Core 2.NBT.B.5Number and Operations in Base Ten

3 class days

Day 1Teach: Open Number Line · Practice on paper (Core page)
Day 2Practice and check: Practice on paper (Easier page, Harder page) · Check-up page
Day 3Reteach and extend: Act on the check-up pages: reteach the children who are not there yet, with the tool and a new page from the maker; the others take a harder page.

Warm up and teach

Open Open Number Line on the projector.

Practice on paper

The Open Number Line
Core page Easier page Harder page

Check-up page

One more page of The Open Number Line to collect at the end of the lesson.

Make more

Make more pages like this with the Number Lines maker.

Lesson 4

Add tens and ones, then put them together

Children add two two-digit numbers within 100 when the ones make a new ten (47 + 38) by adding the tens, adding the ones, and adding the two partial sums (70 + 15).

StandardCommon Core 2.NBT.B.5Number and Operations in Base Ten

2 class days

Day 1Teach: Place Value Lab · Practice on paper (Core page)
Day 2Practice and check: Practice on paper (Easier page, Harder page) · Check-up page

Warm up and teach

Open Place Value Lab on the projector.

Practice on paper

Add Tens and Ones
Core page Easier page Harder page

Check-up page

One more page of Add Tens and Ones to collect at the end of the lesson.

Teacher note

Common mistakes: When the ones add up to more than nine, children write the two sums side by side, so 47 + 38 becomes 715, or they drop the new ten and answer 75. Some add the tens as if they were ones and write 4 + 3 = 7 instead of 40 + 30 = 70.
Words to use: Build 47 in the Place Value Lab and add 38: first 3 tens, then 8 ones. Say: "4 tens and 3 tens are 7 tens: 70. 7 ones and 8 ones are 15 ones. 70 and 15 make 85." Ask: "What is 15? One ten and five ones. Where does that ten go?" Let children draw sticks and dots for one problem on scrap paper and circle ten dots to make a new stick.
What to watch for: Check the first box of each problem: for 40 + 30, did the child write 70 and not 7? The easier page has problems with no new ten, such as 34 + 25. On the harder page children write the tens and ones themselves; the first problem shows how. Check there that the first line says 40 + 30 and not 4 + 3. Not every problem on the harder page makes a new ten; ask children to say which ones will before they add. Have children test an answer against an estimate: 47 + 38 is close to 50 + 40.

Lesson 5

Subtract and open a ten

Children subtract within 100 when there are not enough ones (52 − 27) by regrouping: they open one ten into ten ones in a drawing of sticks and dots.

StandardCommon Core 2.NBT.B.5Number and Operations in Base Ten

2 class days

Day 1Teach: The Exchange Machine · Practice on paper (Core page)
Day 2Practice and check: Practice on paper (Easier page, Harder page) · Check-up page

Warm up and teach

Open The Exchange Machine on the projector.

Practice on paper

Subtract with Regrouping: Tens-and-Ones Mat
Core page Easier page Harder page

Check-up page

One more page of Subtract with Regrouping: Tens-and-Ones Mat to collect at the end of the lesson.

Teacher note

Common mistakes: Children subtract the smaller ones digit from the larger, no matter which number it is in, so 52 − 27 becomes 35. Others draw the ten dots but do not cross out the stick they opened, so they take 2 tens from 5, not from 4. Some open a ten in every problem, even when there are enough ones.
Words to use: The Exchange Machine opens with 48 − 23. "Start at the ones. Are there enough to take 3 away? Yes." Tap "Another sum": 42 − 17. "Enough ones to take 7 away? No, there are only 2." Tap the tens column: one ten crosses over and comes apart into ten ones, and the 4 is crossed out. "We regrouped: 3 tens and 12 ones. It is still 42." Draw the same on the board: four sticks and two dots. Cross out one stick, draw ten dots for it, then cross out 7 dots and 1 stick. "What is left? 2 tens and 5 ones: 25."
What to watch for: The easier page takes away a one-digit number; the page for everyone, a two-digit number. On the harder page, the mat is empty and the child draws the first number. Every page has problems that need no ten opened (two on the first two pages, one on the harder page): there the child marks "yes" and only crosses out. Check the yes/no mark first; a wrong mark explains a wrong answer. A first number with no ones (50 − 4) always needs a ten opened; watch for 54. Have children say what the mat shows after the trade ("4 tens and 10 ones") before they cross anything out.

Lesson 6

Add and subtract vertically

Children add and subtract two-digit numbers written in columns, starting with the ones and writing the traded ten.

StandardCommon Core 2.NBT.B.5Number and Operations in Base Ten

3 class days

Day 1Teach: The Exchange Machine · Practice on paper (Core page)
Day 2Practice and check: Practice on paper (Easier page, Harder page) · Practice on screen · Check-up page
Day 3Reteach and extend: Act on the check-up pages: reteach the children who are not there yet, with the tool and a new page from the maker; the others take a harder page.

Warm up and teach

Open The Exchange Machine on the projector.

Practice on paper

2-Digit Column Addition
Core page Easier page Harder page
2-Digit Column Subtraction
Core page Easier page Harder page

Practice on screen

Tuck's Ten Bundles — Add with Regrouping

Check-up page

One more page of 2-Digit Column Addition to collect at the end of the lesson.

Make more

Make more pages like this with the Addition & Subtraction maker.

Teacher note

Common mistakes: Children write a two-digit sum under the ones column (27 + 15 becomes 312), or they write the new ten and forget to add it. Children who add the tens first have nowhere to put the new ten and leave the tens digit as it was. In subtraction they still take the smaller digit from the bigger one, as with the blocks.
Words to use: Say: "Ones first. 7 and 5 is 12 ones: 1 ten and 2 ones. Write the 2, and write the new ten above the tens." In subtraction: "2 ones take away 7? Not enough ones. Trade one ten for ten ones: now there are 12 ones." Have children say what the small 1 means: "one ten," not "one."
What to watch for: Ask a child to explain the small carried digit. If it is "just a one," go back to blocks and make the trade. Compare the answer with an estimate: "About how much should it be?"

Lesson 7

Add and subtract within 100

Children add and subtract two-digit numbers to fill number walls and to follow a road through a math maze.

StandardCommon Core 2.NBT.B.5Number and Operations in Base Ten

2 class days

Day 1Teach: Practice on paper (Core page)
Day 2Practice and check: Practice on paper (Easier page, Harder page) · Practice on screen · Check-up page

Practice on paper

Number Walls with Two-Digit Answers
Core page Easier page Harder page
Math Maze for 2nd Grade: Add and Subtract Within 100
Core page Easier page Harder page

Practice on screen

Gus's Snack Cart — Add & Subtract Within 100

Check-up page

One more page of Number Walls with Two-Digit Answers to collect at the end of the lesson.

Make more

Make more pages like this with the Logic Puzzles maker.

Lesson 8

Add three and four two-digit numbers

Children add three or four two-digit numbers with a sum within 100 in columns, look for ones that make ten, and write the new tens above the tens column.

StandardCommon Core 2.NBT.B.6Number and Operations in Base Ten

2 class days

Day 1Teach: The Exchange Machine · Practice on paper (Core page)
Day 2Practice and check: Practice on paper (Easier page, Harder page) · Check-up page

Warm up and teach

Open The Exchange Machine on the projector.

Practice on paper

Add Three and Four Two-Digit Numbers
Core page Easier page Harder page

Check-up page

One more page of Add Three and Four Two-Digit Numbers to collect at the end of the lesson.

Teacher note

Common mistakes: Children add the ones, get 18 or 23, and write both digits under the line, so the answer has three digits. Others write the new ten above the tens and forget to add it. When the ones add up to 20 or more, they still write 1 in the small box.
Words to use: On the Exchange Machine, tap "Another sum" five times, until 38 + 25 appears. Fill the outlines in the ones column: "8 and 5 make 13. Only one digit fits under the line." Tap the ones column: ten gather into one new ten on the left. The machine adds two numbers only, so go to the board. Write 18 + 36 + 24 in columns. "Look at the ones: 8, 6, 4. Do two of them make ten? 6 and 4. Ten and 8 more is 18." Write 8 under the ones and a small 1 above the tens. "Now the tens: 1 new ten, and 1, 3, 2. That makes 7 tens." 78.
What to watch for: On the easier page, there are six problems with three numbers; the ones make no new ten and there is no small box. On the page for everyone, four problems have three numbers and four have four; in each, two of the ones digits make ten, and one new ten goes in the small box. On the harder page, every problem has four numbers and the ones make one or two new tens (8 + 9 + 6 + 0 = 23: write 3 under the ones and 2 in the small box). When the ones make exactly 20, a 0 goes under the ones. Ask children to say the sum of the ones before they write. Have them check by adding from the bottom up.

Lesson 9

Why does it work?

Children explain with blocks or a drawing why a way of adding or subtracting within 100 works, and compare two worked ways for the same problem, such as 38 + 25.

StandardCommon Core 2.NBT.B.9Number and Operations in Base Ten

2 class days

Day 1Teach: Place Value Lab · the routine with the class
Day 2Practice: the routine with the class

Warm up and teach

Open Place Value Lab on the projector.

What the class does

Run the lesson as a number talk. Write one problem on the board with two children's ways worked out side by side. For 38 + 25: add tens and ones separately (30 + 20 = 50, 8 + 5 = 13, 50 + 13 = 63) and jump to the next ten (38 + 2 = 40, 40 + 23 = 63). On the second day, for 63 − 28: take away the tens, then the ones (63 − 20 = 43, 43 − 8 = 35) and count up from 28 (28 + 2 = 30, 30 + 33 = 63, so 2 + 33 = 35). Pairs say what each child did and why both ways give the same answer. Then they show 38 + 25 with blocks on the Place Value Lab and 63 − 28 with real blocks. This lesson has no worksheet.

Unit check: before and after

Two short paper checks made from this unit's own worksheets. Give Check A before you teach the unit and Check B after it, and you can see what changed. Each part belongs to one lesson.

Part 1: Lesson 1, A number line that does not start at zero (1 task)
Part 2: Lesson 2, Jumps on the hundreds chart (2 tasks)
Part 3: Lesson 3, Jumps on an open number line (1 task)
Part 4: Lesson 5, Subtract and open a ten (1 task)
Part 5: Lesson 6, Add and subtract vertically (2 tasks)
Part 6: Lesson 8, Add three and four two-digit numbers (3 tasks)

Not in the check: Lesson 4, Lesson 7, Lesson 9. Worksheets that cannot be split into single tasks are left out.

Check A (PDF) · 3 pages Check B (PDF) · 3 pages

Printing a check counts as a download, like any worksheet.

Answer key A Answer key B Teacher pages: points, class record, and what to do next

The answer keys and the teacher pages come with the paid Teacher plan.

This is a classroom check of this unit's lessons. It is not a standardized test, and its points are not a grade.

Unit checks