Objective
Students will be able to fluently add and subtract within 100 using strategies based on place value, properties of operations, and the relationship between addition and subtraction. Students will solve at least 8 out of 10 problems correctly on an exit ticket.
Standards
- CCSS.MATH.CONTENT.2.NBT.B.5 — Fluently add and subtract within 100 using strategies based on place value, properties of operations, and/or the relationship between addition and subtraction.
- CCSS.MATH.CONTENT.2.NBT.B.7 — Add and subtract within 1000, using concrete models or drawings and strategies based on place value.
Materials
- Base-ten blocks (tens rods and ones cubes, 1 set per student)
- Hundred chart (1 per student)
- Number line (posted on wall and individual strips)
- Whiteboard and markers (1 set per student)
- Word problem task cards (12 cards, mixed addition and subtraction)
- Exit ticket worksheet (10 problems)
Warm-Up (5 minutes)
Display three quick mental math problems on the board: 30 + 40, 80 - 50, 25 + 10. Give students 30 seconds each to solve on their whiteboards and hold them up. Review answers as a class and ask volunteers to explain their thinking. Highlight the strategy of adding or subtracting tens first ("I know 3 tens plus 4 tens is 7 tens, which is 70"). This activates place value knowledge students will use throughout the lesson.
Direct Instruction (12 minutes)
Model solving 47 + 35 using base-ten blocks. Break each number into tens and ones: 4 tens + 3 tens = 7 tens, 7 ones + 5 ones = 12 ones. Show how 12 ones becomes 1 ten and 2 ones, so the total is 8 tens and 2 ones = 82. Draw the process on the board alongside the blocks so students see the visual and abstract representations together.
Next, model 73 - 28 using the same blocks. Show that we cannot take 8 ones from 3 ones, so we regroup: break 1 ten into 10 ones, giving us 6 tens and 13 ones. Now subtract: 13 - 8 = 5 ones, 6 tens - 2 tens = 4 tens. Answer: 45. Emphasize the language of "regrouping" rather than "borrowing."
Solve one more example of each (addition with regrouping, subtraction with regrouping) and have students follow along with their own base-ten blocks at their desks.
Guided Practice (10 minutes)
Write 4 problems on the board: 56 + 27, 82 - 39, 64 + 18, 91 - 46. Students solve each problem at their desks using base-ten blocks first, then record the numerical solution on their whiteboards. After each problem, have a student come to the document camera and show their block arrangement while explaining their steps. Correct misconceptions in real time — common errors include forgetting to regroup or subtracting the smaller digit from the larger digit regardless of position (e.g., 82 - 39 = 57 because 9 - 2 = 7).
Independent Practice (10 minutes)
Distribute word problem task cards around the room as a "scoot" activity. Students move from card to card with a recording sheet. Each card has a word problem requiring addition or subtraction within 100 — for example, "Maria had 63 stickers. She gave 27 to her friend. How many stickers does Maria have now?" Students must show their work using a strategy of their choice (blocks, number line, or written algorithm) and write the answer. They complete at least 8 of the 12 cards.
Assessment
- Formative: Monitor whiteboard responses during guided practice. Check for correct regrouping and listen for accurate place value language.
- Summative: Exit ticket with 10 problems (5 addition, 5 subtraction, all requiring regrouping). Score out of 10. Students scoring below 7 join a small reteach group the following day.
Differentiation
- Struggling learners: Provide a place value mat with labeled "tens" and "ones" columns alongside their base-ten blocks. Start with problems that do not require regrouping, then gradually introduce regrouping. Allow use of a hundred chart for counting on/back.
- ELL students: Pre-teach key vocabulary (add, subtract, regroup, tens, ones, total, difference) with visual anchor cards. Simplify word problem language and include pictures. Allow students to explain strategies in their home language to a partner before sharing in English.
- Advanced learners: Extend to three-digit addition and subtraction. Provide challenge problems that require two regroupings (e.g., 148 + 276). Ask them to write their own word problems for a partner to solve.
- Students with IEPs: Provide graph paper to keep digits aligned. Allow use of a calculator to check work after solving. Reduce the exit ticket to 5 problems. Provide step-by-step visual cue cards for the regrouping process.
Closure (3 minutes)
Ask students to turn to a partner and explain one strategy they used today. Then pose a challenge question to the whole class: "If I add 46 + 37, will I need to regroup? How do you know without solving it?" (Yes — because 6 + 7 = 13, which is more than 9.) This reinforces number sense and previews mental estimation strategies.