Introduction: Where Do We Go? (Tell Them What You'll Teach)

Hook: The Busy Bus Stop

Imagine you are waiting at the bus stop. You need to tell the bus driver how many people are waiting, but you don't have time for the exact number! Maybe it's 23 people, but you quickly say, "Oh, about 20!" This is called rounding. Rounding helps us estimate or make a quick, smart guess.

Today, we are going to learn how to make smart guesses with really big numbers, up to 999! We are going to find out which hundred a number is closest to.

Learning Objectives (In Kid Language)

By the end of this lesson, you will be able to:

1. Identify the two hundreds that a three-digit number sits between. (e.g., Is 420 between 400 and 500?)
2. Use the tens digit as a 'helper' to decide if we round up or round down.
3. Correctly round any three-digit number to the nearest hundred.

Success Criteria

You know you are successful when you can point to a number on the number line and correctly name the closest hundred.

The Rounding Climb (Teach It)

I Do: Modeling the Mountain Climber Strategy

(Visual/Auditory Focus)

Step 1: Identifying the Nearest Hundreds Houses (5 minutes)

Let's pretend our number line is a mountain. The hundreds (100, 200, 300, etc.) are the big campsites. Every three-digit number lives between two of those campsites.

• Teacher Modeling Example: Let's look at the number 340.
• First, ask: What hundred is 340 already past? (300)
• Second, ask: What is the next hundred campsite it might climb up to? (400)
• Draw a number line section: Mark 300 on the left and 400 on the right.
• Base Ten Block Connection: Show 3 flats (300) and 4 longs (40). The number 340 is built with 3 hundreds and 4 tens.

Step 2: The Deciding Midpoint (The '50' Rule)

Right in the middle of 300 and 400 is the most important spot: 350. This is the top of the rounding mountain!

• Mark 350 clearly on the number line. Place the toy figure on 350.
• The Mountain Climber Rule: The tens digit tells the number what to do. The tens digit is the 'neighbor' of the hundreds digit.
  • If the number is 50 or more (50, 60, 70, 80, 90), it has enough energy to climb UP to the next hundred. (Climb the toy UP the hill.)
  • If the number is 49 or less (40, 30, 20, 10), it slides back DOWN to the hundred it just passed. (Slide the toy DOWN the hill.)
• Applying the rule to 340: Look at the tens digit: 4. Since 40 is less than 50, 340 slides back down to 300.

We Do: Guided Practice (Visual and Kinesthetic) (8 minutes)

(Interactive/Collaborative Focus)

Let's try rounding the number 575.

1. Identify the Hundreds: What two hundreds does 575 sit between? (500 and 600)
2. Find the Midpoint: What is the deciding number? (550)
3. Look at the Neighbor (The Tens Digit): The tens digit is 7. That means we have 70.
4. Decide the Direction: Is 70 greater than or less than 50? (Greater!)
5. Conclusion: 575 has enough to climb UP to the next hundred, which is 600.
   • Optional Block Practice: Have the learner count out 5 flats and 7 longs, then discuss if 7 longs are closer to 10 longs (which would be 600) or 0 longs (which would be 500).

Let's try rounding 120.

1. Identify the Hundreds: (100 and 200)
2. Find the Midpoint: (150)
3. Look at the Neighbor: The tens digit is 2 (20).
4. Decide the Direction: Is 20 greater than or less than 50? (Less!)
5. Conclusion: 120 slides back DOWN to 100.

You Do: Independent Practice and Explanation (7 minutes)

(Check for Understanding/Formative Assessment)

Now it's your turn to be the rounding expert! Use your number line template.

Task 1: Round 485.

1. Draw the two hundreds (400 and 500).
2. Mark the midpoint (450).
3. Plot 485.
4. Tell me your thinking: What is the closest hundred and why? (Expected Answer: 500, because the 8 in the tens place means 80, which is more than 50, so we climb up.)

Task 2: Round 709.

1. Draw the two hundreds (700 and 800).
2. Mark the midpoint (750).
3. Plot 709.
4. Tell me your thinking: What is the closest hundred and why? (Expected Answer: 700, because the 0 in the tens place means 9, which is much less than 50, so we slide down/stay.)

Conclusion: Recap and Challenge (Tell Them What You Taught)

Quick Recap

Let’s quickly review the two most important steps when rounding to the nearest hundred:

1. You must find the two nearest hundreds (the campsites).
2. You must check the 'neighbor'—the tens digit! If the tens digit is 5 or more (50, 60, 70...), you round up. If it is 4 or less (40, 30, 20...), you round down.

Summative Assessment: Rounding Challenge

Quickly round these numbers in your head or on scratch paper:

• 615 rounds to... (600)
• 978 rounds to... (1000)
• 250 rounds to... (300) [Reinforce that 50 always rounds UP!]

Differentiation and Extension

• Scaffolding (For Struggle): If the learner struggled, focus only on the tens place. Provide physical base ten blocks for every problem and require them to build the number before deciding. Use only numbers where the tens place is clearly high (e.g., 280) or clearly low (e.g., 210) until the concept of 50 is solid.
• Extension (For Mastery): Challenge the learner to round four-digit numbers to the nearest thousand (e.g., Round 4,320 to the nearest thousand. Now they look at the hundreds place!). Or, have them create a 'rounding puzzle' for an adult to solve, listing five numbers rounded to the nearest hundred.