Integer Clinic Teacher Guide Integer Clinic
Teacher Facilitation Guide
Grade 8 Review
Learning Objective
Students will identify, diagnose, and correct common procedural and conceptual errors in integer subtraction (specifically negative minus negative) by applying the "Add the Opposite" rule and the debt analogy.
Supplies Needed
Red Pens (1 per student)
Error Doctor Worksheets
Classroom Slide Deck
Mini-whiteboards (optional)
Lesson Timeline
5 MIN
The Silent Diagnosis (Warm-up)
Display the "sick" problem: \(-10 - (-5) = -15\). Students identify the mistake silently. Ask for volunteers to explain why a student might make this mistake (e.g., they just added the numbers and kept the negative sign).
10 MIN
Source of Truth (Video)
Watch "Subtracting Negative from a Negative" by Mr. J. Students use their worksheet to take notes on the rewriting step . Use the pause points in the slide deck to check for understanding.
20 MIN
The Error Doctor (Main Activity)
Distribute Red Pens . Students work through the "Patient Ward" on the worksheet. They must circle the specific sign or calculation error, explain the rule broken, and provide the correct "cured" solution.
10 MIN
Medical Board Debrief (Closure)
Discuss the "Deadliest Error" (the most common mistake). Revisit the debt analogy: why does removing a negative increase value?
Doctor's Consultation Prompts
The Strategy
"Why is 'Add the Opposite' safer than trying to subtract in your head?"
The Concept
"In real life, when is 'taking away a bad thing' actually a good thing?"
The Visualization
"If you're facing left and you walk backward, where do you end up?"
The Warning
"What is the most 'contagious' mistake we saw today?"
Extension Activity: The Tricky Quiz
Challenge students to create a "Patient Profile" for their partner. They write 3 problems with subtle, purposeful mistakes. Their partner must then "diagnose" them. This encourages high-level thinking by requiring students to anticipate potential errors.
Integer Clinic Slides Integer Clinic
Specialty: Negative Subtraction
Welcome, Error Doctors
The Silent Diagnosis
Patient Case #105:
-10 - (-5) = -15
Analyze the work silently.
Where is the error?
The Source of Truth
Consulting with Specialist: Mr. J
Doctor's Orders:
In your notes, capture the "Rewriting Step" exactly as shown.
Listen For:
The phrase "Add the Opposite". Why do we do it?
Video Loading...
Training Session LIVE CONSULTATION
Embedded media
Pause & Predict
Mr. J is about to rewrite -5 - (-9).
Challenge:
How will he rewrite it? Show me on your desk.
Clinical Reasoning
The answer is 4.
Critical Question:
Why did the number get BIGGER?
Think: Money & Debt
Paging Dr. [Your Name]
The Patient Ward is Full
Instructions:
1. Use your Red Pen
2. Circle the exact error
3. Cure the problem
Post-Op Debrief
The Deadliest Error
Of all the patients we saw today, which mistake was the most common? Why do our brains keep doing it?
The Success Rate
Who found a mistake that was "hidden" really well? What tip would you give a junior doctor?
Error Doctor Worksheet The Patient Ward
Integer Clinic • Medical Record #8-INT-2026
ATTENDING PHYSICIAN:
DATE: JANUARY 19, 2026
Source of Truth: Video Notes
Record the exact rewriting step shown in the video:
PROBLEM 1:
-5 - (-9)
PROBLEM 2:
-23 - (-10)
The Debt Analogy: Subtracting a negative is like a debt, which is a thing for your bank account.
Diagnosis & Cure (Red Pen Required)
Patient Case (Mistake)
Circle
Medical Reasoning (Rule Broken)
The Cure (Correct Work)
-7 - (-3) = -10
-12 - (-20) = -32
-5 - (-5) = -10
-1 - (-6) = -5
Post-Op Reflection
Summary Report:
Why does subtracting a negative number always increase the value of the problem? Use the debt analogy or the number line to explain your thinking.
Extension: The Tricky Quiz
Challenge Level: Specialist
Create your own "Sick Problem" below. Write a problem and a plausible mistake . Then, trade with a partner to see if they can diagnose it!
Create the "Sick" Patient
____ - (____) = ____
Make it look real!
Partner's Diagnosis
Error Doctor Answer Key The Patient Ward
Official Answer Key • Medical Board Certified
STATUS: ALL PATIENTS CURED
DATE: JANUARY 19, 2026
Source of Truth: Video Notes
PROBLEM 1:
-5 - (-9) -5 + 9 = 4
PROBLEM 2:
-23 - (-10) -23 + 10 = -13
The Debt Analogy: Subtracting a negative is like removing a debt, which is a positive thing for your bank account.
Diagnosis & Cure Key
Patient Case
Error
Diagnosis (Rule Broken)
The Cure (Work)
-7 - (-3) = -10
-10
Rule Broken:
The doctor didn't "Add the Opposite". They treated it as \(-7 - 3\). They failed to change the second sign.
-7 + (+3) = -4
-12 - (-20) = -32
-32
Rule Broken:
Sign error after rewriting. \(-12 + 20\) should result in a positive value because \(20 > 12\). The value must increase.
-12 + 20 = 8
-5 - (-5) = -10
-10
Rule Broken:
Additive Inverse Error. Subtracting a number from itself should always equal zero, but they ignored the negative signs.
-5 + 5 = 0
-1 - (-6) = -5
-5
Rule Broken:
Directional error. They correctly knew to subtract 1 and 6 but gave it the wrong sign. \(6 - 1 = 5\), not \(-5\).
-1 + 6 = 5
Attending Physician Summary (Reflection Answer)
"Subtracting a negative increases value because we are removing a 'negative' force. In the debt analogy, removing a $50 debt is the same as gaining $50 in cash. On a number line, facing the negative direction (left) and walking backward results in moving toward the positive (right)."
