← Think + AI Free tool · Grades 7–12

Side by Side

Students compare two solutions, two cases, two concepts or two sources placed next to each other. They sort what is only in A, in both and only in B, write the rule they found, and then try it on a new case.

About 10 minutes to prepare, 15 minutes in class, no student devices needed.

Build your pair

Do not include student names or student work. The prompt only needs your subject, topic and grade.

How hard should the difference be to see?

Fill in subject and topic to see your prompt.

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Fifteen minutes in the lesson

The AI's reply starts with a block headed FOR STUDENTS. Copy only that block: print it or show it on the board, with A and B visible at the same time, and hand out the student sheet. Students work in pairs or small groups.

  1. Compare (6 min). Fill in the three columns: only in A, in both, only in B.
  2. Write the rule (3 min). In one or two sentences, say what the comparison shows.
  3. Try it on case C (4 min). Use the rule on the new case and explain the answer.
  4. Think back (2 min). Each student writes one sentence about how they thought, not what they found.

Let students find the difference and write the rule before you say anything; then confirm or sharpen their rule with the key. Before you print, read the TEACHER KEY and check everything listed under CHECK. If A and B differ in more than the intended way, generate a new pair. The AI prepares; you decide.

The five pair types

Each type is a kind of comparison that works across subjects. Open a card to see a worked example as a real pair, with the teacher's key.

Pair 1

Two ways to the same answer

Two correct methods reach the same answer by different routes.

Strong

What to look for

  • Where do the two methods first part ways?
  • What does each method save, and what does it cost?
  • When would you choose each one?
Worked example with the teacher's key

Maths · Grade 8 · Easier to see

Task: Solve 3(x + 2) = 15.

A · Alex

3x + 6 = 15
3x = 9
x = 3

B · Sam

x + 2 = 5
x = 3

Teacher's key

Only A

Alex multiplies out the brackets first, then undoes the + 6 and the × 3. Three lines.

Both

The same answer, x = 3. Both do the same thing to both sides, so the equation stays balanced.

Only B

Sam divides both sides by 3 first, because 15 divides exactly by 3. Two lines.

The rule
Dividing first is quicker when the number outside the brackets divides the other side exactly. Otherwise, multiplying out first avoids working with fractions early on.
Case C
Solve 3(x + 4) = 20. Which method would you use, and why?
Case C answer
Multiply out first, because 20 does not divide exactly by 3: 3x + 12 = 20, 3x = 8, x = 8/3. Dividing first gives x + 4 = 20/3, and then you have to work out 20/3 − 4.
Probe
Change 3(x + 2) = 15 so that Sam's first step becomes the harder one. What did you change?
Think back
Before today, my first step was always ___.
Use this pair
Pair 2

Right next to wrong

A correct and an incorrect solution to the same task, side by side.

Promising

What to look for

  • Find the first line where the two solutions differ.
  • Say which rule the wrong step breaks.
  • Check that the correct solution keeps that rule.
Worked example with the teacher's key

Chemistry · Grade 9 · Easier to see

Task: Balance the equation for hydrogen burning in oxygen to make water: H₂ + O₂ → H₂O.

A · Mia

2H₂ + O₂ → 2H₂O
Left: 4 H, 2 O. Right: 4 H, 2 O.

B · Leo

This solution has an error.
H₂ + O₂ → H₂O₂
Left: 2 H, 2 O. Right: 2 H, 2 O.

Teacher's key

Only A

Mia changes the coefficients, the numbers in front of the formulas, and keeps the product as H₂O.

Both

Both start from the same reactants, and both end with the same number of each atom on each side.

Only B

Leo changes a subscript, the small number inside the formula, so the product becomes H₂O₂, hydrogen peroxide, not water.

The rule
Balance an equation by changing the coefficients (the numbers in front of the formulas), never the subscripts (the small numbers inside them). Changing a subscript changes the substance.
Case C
Balance the equation for magnesium burning in oxygen: Mg + O₂ → MgO.
Case C answer
2Mg + O₂ → 2MgO. Writing MgO₂ would balance the oxygen but describe a different substance.
Probe
Leo's equation is balanced. So why is it still wrong for this task?
Think back
The difference I nearly missed was ___.
Use this pair
Pair 3

One thing changed

Two cases are identical except for one thing.

Promising

What to look for

  • Name the one thing that is different.
  • Compare what happened, not just what was done.
  • Ask what the difference in results tells you about that one thing.
Worked example with the teacher's key

Biology · Grade 7 · Harder to see

Task: Two dishes of cress seeds were set up on Monday. Compare them on Friday.

A · Clear box

Cress seeds on damp cotton wool, on a windowsill at room temperature, under a clear plastic box. On Friday the seeds have sprouted: short seedlings with green seed leaves.

B · Light-proof box

Cress seeds on damp cotton wool, on a windowsill at room temperature, under a light-proof box. On Friday the seeds have sprouted: tall, thin seedlings with pale yellow seed leaves.

Teacher's key

Only A

Light through the clear box. The seedlings are short with green seed leaves.

Both

Water, warmth, a box over the dish, the same windowsill and the same seeds. Both dishes have sprouted.

Only B

Darkness under the light-proof box. The seedlings are tall and thin with pale yellow seed leaves.

The rule
The cress seeds sprouted in both dishes, so cress seeds do not need light to sprout: the seed uses its own stored food. Light matters afterwards, for the green leaves that make new food.
Case C
Dish C is set up like the other two, with damp cotton wool, but it is left in a dark cupboard. Will the seeds sprout, and what will the seedlings look like on Friday?
Case C answer
Yes, they will sprout, because cress seeds do not need light to sprout. Without light the seedlings will be tall, thin and pale, like those under the light-proof box.
Probe
The two dishes look very different. Why is "light makes seeds sprout" still the wrong conclusion?
Think back
At first I looked at ___ instead of what both dishes had in common.
Use this pair
Pair 4

Two concepts that are easily confused

Two related ideas that students often mix up, shown in the same context.

Promising

What to look for

  • List what each one has that the other does not.
  • Find what they share, so you know why they get mixed up.
  • Make a quick test you could use next time.
Worked example with the teacher's key

English · Grade 7 · Easier to see

Task: Two sentences describe the same hot classroom.

A · Simile

The classroom was like an oven.

B · Metaphor

The classroom was an oven.

Teacher's key

Only A

The word "like". It says the classroom resembles an oven.

Both

Both compare the classroom to an oven to show how hot it was. Neither is meant literally.

Only B

No comparing word. It says the classroom is an oven.

The rule
A simile compares two different things using "like" or "as". A metaphor says one thing is another. Both are comparisons, not literal statements.
Case C
"The test was a mountain to climb." Simile or metaphor?
Case C answer
A metaphor: there is no "like" or "as", and it says the test is a mountain.
Probe
Which sentence is stronger, and why might a writer still choose the simile?
Think back
The test I will use next time is ___.
Use this pair
Pair 5

Two sources on the same event

Two sources describe the same event but differ in when, by whom or why they were written, which changes how far we can trust them.

Promising

What to look for

  • Who wrote each source, when and why?
  • Which details agree, and which do not?
  • Which source would you trust for which question?
Worked example with the teacher's key

History · Grade 9 · Harder to see

Task: Two accounts of the first morning of a strike at a cotton mill in 1912. Both were written for this task.

A · Diary, 1912

Mary Dent, mill worker, private diary, 4 May 1912: "Went to the gate at six. Perhaps two hundred of us. Mr Hale, the owner, came out and said the mill would close if we did not go in. Nobody moved. Rain all afternoon." (Written for this task.)

B · Memoir, 1950

Mary Dent, memoir published in 1950: "I shall never forget the morning a thousand of us stood at the gates in brilliant sunshine, and the owner fled before our courage." (Written for this task.)

Teacher's key

Only A

Written the same day, in a private diary. Small, plain details: the time, the rain, about two hundred people.

Both

The same eyewitness and the same event: a crowd at the gate and the owner facing them.

Only B

Written 38 years later, for readers. Bigger numbers, sunshine and a heroic story.

The rule
Even the same eyewitness becomes less reliable on details when writing long after the event for an audience. For details, prefer accounts written close to the event, and be more cautious with any account written to persuade; later accounts show how the event was remembered.
Case C
A union leaflet printed the next day, calling on other workers to join, says "thousands stood firm at Hale's gate". How far would you trust its number?
Case C answer
Not far. It was written close to the event, but to persuade, so the number may be inflated. Check it against Source A.
Probe
What can Source B tell us that Source A cannot?
Think back
I trusted ___ before I checked when and why it was written.
Use this pair

Upper-secondary variant

Older students can make a pair themselves in the school's approved AI tool, then swap with another group, who compare it with the same sheet. Making a pair with one difference that matters is itself a strong test of understanding.

  1. Each group chooses a pair type and pastes the prompt into the school's approved AI tool, adding the lesson topic.
  2. The group checks that the pair has the difference they intended, and writes their own key on a separate sheet.
  3. Groups swap pairs and work through the sheet: the three columns, the rule and a case C they make up for each other.
  4. Close with Think back: one sentence about how they thought.
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Only with the school's approved AI tool, and only where the age rules below allow it.

How strong is the evidence?

  • Strong Meta-analyses or several classroom experiments show that learning by this kind of comparison works.
  • Promising Comparison works in related research, but few school studies test this exact kind of pair.

Labels rate the research on teaching with comparisons regularly, not a single use. One Side by Side is one small piece of that practice.

  • Strong Learning by comparing cases. Comparing cases side by side improves learning more than other ways of studying the same material, such as studying cases one at a time (Alfieri et al. 2013, a meta-analysis of 57 experiments, d ≈ 0.50). Learning was greater when the principle was given after the comparison, which is why students write the rule before the teacher confirms it. Source: Alfieri, Nokes-Malach & Schunn 2013, Educational Psychologist
  • Strong Comparing solution methods. In randomized classroom studies with Grade 7 and 8 algebra students, comparing two solution methods side by side built more flexible problem solving than studying the methods one at a time (Rittle-Johnson & Star 2007) or comparing problems solved the same way (2009). Gains in conceptual knowledge appeared in the second study but not the first. Source: Rittle-Johnson & Star 2007, Journal of Educational Psychology, Rittle-Johnson & Star 2009, Journal of Educational Psychology
  • Promising Comparing correct and incorrect solutions. Comparing a correct and an incorrect example helped primary students learn decimals and reduced misconceptions more than comparing two correct examples (Durkin & Rittle-Johnson 2012), and incorrect examples supported conceptual understanding in algebra classes (Booth et al. 2013). Results have not replicated consistently. Source: Durkin & Rittle-Johnson 2012, Learning and Instruction, Booth et al. 2013, Learning and Instruction
  • Promising Contrasting cases with one change. Analysing contrasting cases before a lecture helped college students notice what matters and learn more from the explanation that followed (Schwartz & Bransford 1998). Source: Schwartz & Bransford 1998, Cognition and Instruction
  • Promising Concepts that are easily confused. Mixing examples from different categories (interleaving) helps learners tell them apart (Brunmair & Richter 2019, a meta-analysis of 59 studies, g = 0.42), especially when the categories are similar. Few studies have tested confusable concept pairs side by side in school. Source: Brunmair & Richter 2019, Psychological Bulletin
  • Promising Comparing sources. In a six-month quasi-experiment in five urban high schools, Grade 11 students taught with document-based lessons, which involved reading and questioning several sources on the same event, outperformed control classes in historical thinking, factual knowledge and reading comprehension (Reisman 2012). The study tested the whole curriculum, not source comparison alone. Source: Reisman 2012, Cognition and Instruction

In the classroom. In a video study of eighth-grade maths lessons, teachers in Hong Kong and Japan used analogies as often as US teachers but supported them more, for example by keeping both cases visible at the same time and using gestures to show what to compare (Richland, Zur & Holyoak 2007). Side by Side builds those supports into the sheet.

Sources

For research on many other teaching strategies, see the Evidence Toolkit on this site.

AI tools and age rules

You use AI to prepare the pair. Your students do not need to. If older students use AI themselves, as in the upper-secondary variant, these rules apply (October 2026):

Rules differ between countries and change often. Check your own national rules and your school policy before students use any AI tool.

Downloads

The student sheet is one A4 page: room for A and B on top, the three columns, the rule box, case C and Think back. The card deck has all five pair types with their worked examples, plus a fill-in prompt for when you are offline. Free to print and share.

Download the student sheet (PDF) Download the card deck (PDF)