Story Architect Guide
Story Architect Guide
Subtraction Bar Models • 2nd Grade Math
Teacher Resource
Learning Objective
Students will be able to reverse-engineer subtraction bar models by writing creative word problems that match given numerical structures (part-whole and comparison models).
Pacing
- Hook: 5 min
- Viewing: 5 min
- Activity: 25 min
- Extension: 5 min
1. The Silent Hook (5 min)
Display the "Silent Model" slide. It shows a total of 20, one part of 5, and a missing part.
"Look at this blueprint. There are no words yet, but there is a story hiding inside. Who can guess what happened? Maybe it's about cookies, or space aliens, or lost buttons."
2. Video Viewing (5 min)
Watch "Subtraction Within 20 with Bar Models". Focus on the "Tag Sale" segment (1:35-2:47) to see a part-whole model in action.
0:26
Pause: Ask students for keywords. "What does 'fewer' tell us? Will the answer be bigger or smaller than 19?"
1:51
Pause: Comparison vs. Part-Whole. "Are we comparing two different groups (chickens), or splitting one total (money)?"
3. Main Activity (25 min)
Students receive the Reverse Engineering Worksheet. They must look at the bar models and write a story to fit the numbers.
Check for Logic
Ensure the "story question" actually asks for the missing part shown in the model.
Encourage Creativity
Move beyond "I had 10 apples." Encourage themes like robots, ocean animals, or sports.
Vocabulary to Listen For
Fewer
Comparison word
Difference
Result of subtraction
Part-Whole
Splitting one total
Comparison
Two separate bars
Story Blueprints Presentation
Math Workshop
Story
Blueprints
Drawing Stories from Bar Models
Think
Model
Write
The Mystery Model
What is the story hiding in this blueprint?
20
5
?
"Once upon a time, there were 20..."
Watch & Learn
Model Detectives
Embedded media
Look for the Part-Whole model (one bar) and the Comparison model (two bars).
Two Types of Blueprints
Part-Whole
One big bar split into pieces. We know the Total and one Part.
?
Finding a Piece
Comparison
Two bars of different lengths. We look for the Difference (the gap).
?
Finding the Gap
Your Mission
1
Observe
Look at the bar model on your page. Is it Comparison or Part-Whole?
2
Write
Create a story about anything you want that fits those numbers!
3
Solve
Show the math equation and find the final answer.
Don't forget the question mark!
Story Blueprint Worksheet
Story Blueprint
Reverse Engineer the Math!
Architect:
Date:
Instructions: Look at the bar model. Write a creative story that matches the numbers. Then, solve it!
Model 1: Part-Whole
18
7
?
Write your Story:
Equation:
Final Answer:
Model 2: Comparison
15
?
6
Write your Story:
Equation:
Final Answer:
Model 3: Part-Whole
25
?
12
Write your Story:
Equation:
Final Answer:
Model 4: Comparison
32
?
9
Write your Story:
Equation:
Final Answer:
Story Blueprint Answer Key
Answer Key
Story Blueprint Worksheet
Teacher Only
#1
Model 1: Part-Whole (18, 7, ?)
Sample Story:
"There were 18 space robots on the moon. 7 robots flew back to Earth. How many robots are still on the moon?"
Equation:
18 - 7 = 11
Answer:
11 robots
#2
Model 2: Comparison (15, 6, ?)
Sample Story:
"Leo found 15 seashells. Mia found 6 fewer seashells than Leo. How many seashells did Mia find?"
Equation:
15 - 6 = 9
Answer:
9 seashells
#3
Model 3: Part-Whole (25, 12, ?)
Sample Story:
"Farmer Brown had 25 apples in a basket. 12 apples were red and the rest were green. How many apples were green?"
Equation:
25 - 12 = 13
Answer:
13 green apples
#4
Model 4: Comparison (32, 9, ?)
Sample Story:
"A blue car is 32 feet long. A red car is 9 feet shorter than the blue car. How long is the red car?"
Equation:
32 - 9 = 23
Answer:
23 feet
