• Add three-digit numbers using the standard algorithm with regrouping(3.NBT.A.2)
• Explain regrouping using place value understanding
• Check addition using estimation strategies

• Base-ten blocks (1 set per pair)
• Place value charts (1 per student)
• Whiteboards and markers (1 per student)

Quick mental addition to activate prior knowledge

• Display: 45 + 38. Ask students to solve mentally and share strategies.
• Record strategies on the board (making tens, compensation, etc.)
• Display: 156 + 200. Discuss why this is easier than 156 + 198.
• Introduce today's focus: What happens when we need to regroup in larger numbers?

Direct instruction on the standard algorithm with manipulatives

• Model 347 + 285 using base-ten blocks on the document camera
• Show combining ones: 7 + 5 = 12 ones, regroup as 1 ten and 2 ones
• Show combining tens: 4 + 8 + 1 = 13 tens, regroup as 1 hundred and 3 tens
• Show combining hundreds: 3 + 2 + 1 = 6 hundreds
• Connect concrete model to written algorithm step-by-step
• Work through 2 more examples with increasing student participation

Students work in pairs to solve problems with manipulatives

• Partners solve: 463 + 279, 528 + 394, 187 + 456
• One partner builds with blocks, other records the algorithm
• Switch roles for each problem
• Circulate and address misconceptions
• Bring class together to discuss strategies and common errors

Students work independently on addition problems

• Students complete 6-8 three-digit addition problems
• Include problems requiring regrouping in ones only, tens only, and both
• Challenge: Create your own problem that requires regrouping twice
• Early finishers can check work using estimation or inverse operation

• Ask: What is regrouping and why do we do it?
• Have students share one strategy that helped them today
• Preview: Tomorrow we'll apply this to real-world word problems
• Exit ticket: Solve one problem and explain your thinking