Compare the product with a positive starting quantity by comparing its factor with one.
The original lesson PDFs remain version 1.0.0. This supplement adds diagnostic probes, teaching responses, and question-specific rubrics. Use the supplement below for the updated guidance.
Ask for an explanation or drawing before choosing a response. A wrong answer alone does not identify its cause.
Question-by-question misconception guide and open-response criteria
Use these as follow-up prompts, then examine the learner’s model or explanation. Open responses may differ from the sample while satisfying the criteria.
c1: Calculate 3/4 × 1/2. Show a model or your reasoning.
Watch for: Assumes multiplication always enlarges a positive amount.
Try: Keep a 3/4-meter ribbon as the starting amount. Compare half a copy, one copy, and two copies. Record 3/8, 3/4, and 3/2 meters, then relate each change to a factor below, equal to, or above one.
c2: Calculate 3/4 × 1. Show a model or your reasoning.
Watch for: Assumes multiplication always enlarges a positive amount.
Try: Keep a 3/4-meter ribbon as the starting amount. Compare half a copy, one copy, and two copies. Record 3/8, 3/4, and 3/2 meters, then relate each change to a factor below, equal to, or above one.
c3: Calculate 3/4 × 2. Show a model or your reasoning.
Watch for: Assumes multiplication always enlarges a positive amount.
Try: Keep a 3/4-meter ribbon as the starting amount. Compare half a copy, one copy, and two copies. Record 3/8, 3/4, and 3/2 meters, then relate each change to a factor below, equal to, or above one.
c4: Calculate 2/3 × 3/4. Show a model or your reasoning.
Watch for: Assumes multiplication always enlarges a positive amount.
Try: Keep a 3/4-meter ribbon as the starting amount. Compare half a copy, one copy, and two copies. Record 3/8, 3/4, and 3/2 meters, then relate each change to a factor below, equal to, or above one.
c5: Calculate 2/3 × 3/2. Show a model or your reasoning.
Watch for: Assumes multiplication always enlarges a positive amount.
Try: Keep a 3/4-meter ribbon as the starting amount. Compare half a copy, one copy, and two copies. Record 3/8, 3/4, and 3/2 meters, then relate each change to a factor below, equal to, or above one.
c6: Calculate 5/6 × 2/5. Show a model or your reasoning.
Watch for: Assumes multiplication always enlarges a positive amount.
Try: Keep a 3/4-meter ribbon as the starting amount. Compare half a copy, one copy, and two copies. Record 3/8, 3/4, and 3/2 meters, then relate each change to a factor below, equal to, or above one.
c7: Calculate 4/5 × 5/4. Show a model or your reasoning.
Watch for: Assumes multiplication always enlarges a positive amount.
Try: Keep a 3/4-meter ribbon as the starting amount. Compare half a copy, one copy, and two copies. Record 3/8, 3/4, and 3/2 meters, then relate each change to a factor below, equal to, or above one.
c8: Calculate 7/8 × 4/3. Show a model or your reasoning.
Watch for: Assumes multiplication always enlarges a positive amount.
Try: Keep a 3/4-meter ribbon as the starting amount. Compare half a copy, one copy, and two copies. Record 3/8, 3/4, and 3/2 meters, then relate each change to a factor below, equal to, or above one.
s1: Calculate 1/2 × 1/2. Show a model or your reasoning.
Watch for: Assumes multiplication always enlarges a positive amount.
Try: Keep a 3/4-meter ribbon as the starting amount. Compare half a copy, one copy, and two copies. Record 3/8, 3/4, and 3/2 meters, then relate each change to a factor below, equal to, or above one.
s2: Calculate 1/2 × 1. Show a model or your reasoning.
Watch for: Assumes multiplication always enlarges a positive amount.
Try: Keep a 3/4-meter ribbon as the starting amount. Compare half a copy, one copy, and two copies. Record 3/8, 3/4, and 3/2 meters, then relate each change to a factor below, equal to, or above one.
s3: Calculate 1/2 × 2. Show a model or your reasoning.
Watch for: Assumes multiplication always enlarges a positive amount.
Try: Keep a 3/4-meter ribbon as the starting amount. Compare half a copy, one copy, and two copies. Record 3/8, 3/4, and 3/2 meters, then relate each change to a factor below, equal to, or above one.
s4: Calculate 3/4 × 1/2. Show a model or your reasoning.
Watch for: Assumes multiplication always enlarges a positive amount.
Try: Keep a 3/4-meter ribbon as the starting amount. Compare half a copy, one copy, and two copies. Record 3/8, 3/4, and 3/2 meters, then relate each change to a factor below, equal to, or above one.
h1: Why is 3/4 × 1/2 smaller than 3/4?
Watch for: Assumes multiplication always enlarges a positive amount.
Try: Keep a 3/4-meter ribbon as the starting amount. Compare half a copy, one copy, and two copies. Record 3/8, 3/4, and 3/2 meters, then relate each change to a factor below, equal to, or above one.
Look for in the response:
- Interpret the factor 1/2 as taking half of the positive amount 3/4.
- Show or state that the result is 3/8.
- Explain that half of a positive amount is smaller than the starting amount.
h2: Give a counterexample to multiplication always makes numbers bigger.
Watch for: Assumes multiplication always enlarges a positive amount.
Try: Keep a 3/4-meter ribbon as the starting amount. Compare half a copy, one copy, and two copies. Record 3/8, 3/4, and 3/2 meters, then relate each change to a factor below, equal to, or above one.
Look for in the response:
- Provide a valid multiplication example using a positive factor below one.
- Compute the product correctly.
- Compare the product with the starting positive amount and show that it is smaller.
h3: What happens when a positive quantity is scaled by one?
Watch for: Assumes multiplication always enlarges a positive amount.
Try: Keep a 3/4-meter ribbon as the starting amount. Compare half a copy, one copy, and two copies. Record 3/8, 3/4, and 3/2 meters, then relate each change to a factor below, equal to, or above one.
Look for in the response:
- Specify a positive starting quantity.
- State that multiplying it by one preserves its value.
- Explain using one complete copy of that quantity.
h4: Predict without computing whether 7/8 × 4/3 exceeds 7/8.
Watch for: Assumes multiplication always enlarges a positive amount.
Try: Keep a 3/4-meter ribbon as the starting amount. Compare half a copy, one copy, and two copies. Record 3/8, 3/4, and 3/2 meters, then relate each change to a factor below, equal to, or above one.
Look for in the response:
- Identify the scale factor 4/3 as greater than one.
- Predict the product exceeds the starting 7/8.
- Justify the prediction from scaling rather than requiring the exact product.
e1: Calculate 3/4 × 1/2. Show a model or your reasoning.
Watch for: Assumes multiplication always enlarges a positive amount.
Try: Keep a 3/4-meter ribbon as the starting amount. Compare half a copy, one copy, and two copies. Record 3/8, 3/4, and 3/2 meters, then relate each change to a factor below, equal to, or above one.
e2: State the scaling rule for positive amounts.
Watch for: Assumes multiplication always enlarges a positive amount.
Try: Keep a 3/4-meter ribbon as the starting amount. Compare half a copy, one copy, and two copies. Record 3/8, 3/4, and 3/2 meters, then relate each change to a factor below, equal to, or above one.
Look for in the response:
- For a positive starting amount, state that a positive factor below one makes it smaller.
- State that a factor of one preserves it.
- State that a factor greater than one enlarges it; connect the half-factor case to e1.