Weighing Up Several Ideas
A 55-minute Grade 3 lesson on generating several possible solutions and comparing them against the criteria and constraints.
Weighing Up Several Ideas is a free 55-minute Grade 3 to Grade 5 science lesson plan for Common Core standard 3-5-ETS1-2 — compare several possible solutions against the criteria and the constraints. It is timed across 5 sections, gives the exact wording to use where the wording carries the mathematics, names 3 misconceptions with the teaching move that addresses each, and ends with an exit ticket and a printable worksheet with its answer key.
- Grade:
- Grade 3 to Grade 5
- Length:
- 55 minutes
- Standard:
- 3-5-ETS1-2
Grade 3 to Grade 5 · Engineering Design
3-5-ETS1-2
Generate and compare multiple possible solutions to a problem based on how well each is likely to meet the criteria and constraints of the problem.
Objective
Students will be able to compare three solutions against a written brief and justify a choice.
Students are successful when they can
- Generates more than one solution.
- Scores each against every criterion and constraint.
- Justifies the choice from the scores.
What you need
- The brief from the previous lesson
- A comparison grid with a row per solution
- The printable practice sheet linked at the end of this plan
The lesson
Warm-up
5 min- Take the first solution anybody offers and ask what else could work.
- Insist on three before discussing any of them.
Teach — the grid does the deciding
14 min- Write the three solutions down the side and the criteria along the top.
- Score the first solution against each criterion honestly.
- Do the same for the other two.
- Add the constraint columns and mark any solution that breaks one.
- Say the rule: a solution that fails a constraint is out, however well it scores.
- Read the winner off the grid and say what made it win.
“Which criterion is that failing? Mark it.”
Investigate — build the grid
19 min- Groups generate three solutions to their brief.
- They build a comparison grid and score every cell.
- They rule out any that break a constraint.
- They write a sentence justifying the winner from the grid.
Independent practice
14 min- Students complete the 'Weighing Up Several Ideas' page.
- Check the justification refers to the criteria.
Close
3 min- Ask whether the winner was anybody's first idea.
What goes wrong, and why
Each of these is a reasoning error rather than carelessness. The fix addresses the reasoning.
Generates one solution and refines it.
Why: The first idea was good.
Fix: Three first. The comparison is what the standard asks for.
Chooses the favourite and scores it kindly.
Why: The grid confirms the preference.
Fix: Score every cell before looking at totals.
Keeps a solution that breaks a constraint.
Why: It scores well on criteria.
Fix: A constraint is not a preference. It is out.
If they are not there yet
- Two solutions and two criteria.
- A grid with the first row scored.
If they finish early
- Combine the best parts of two solutions and score the result.
- Say which criterion split the three most.
- Add a criterion that would change the winner.
Exit ticket
Three designs are compared. One meets every criterion but costs eight pounds against a five pound limit. What happens to it?
What to look for: It is ruled out, because it breaks a constraint however well it meets the criteria. Choosing it anyway means the constraint rule needs another run.
Printable practice for 3-5-ETS1-2
Free to print and copy, answer key included. Each sheet can generate a fresh set of problems for a retake.
- Weighing Up Several IdeasCircle the best answer.
Questions about Weighing Up Several Ideas
How long does the Weighing Up Several Ideas lesson take?
55 minutes, split across 5 timed sections: warm-up 5 min, teach 14 min, investigate 19 min, independent practice 14 min, close 3 min. The minutes are stated per section and add up to the stated length, so the plan can be cut or extended at a section boundary rather than abandoned halfway.
Which standard does Weighing Up Several Ideas teach?
3-5-ETS1-2 — 3-5-ETS1-2, Engineering Design for Grade 3 to Grade 5: “Generate and compare multiple possible solutions to a problem based on how well each is likely to meet the criteria and constraints of the problem.” In plain terms, compare several possible solutions against the criteria and the constraints.
What do I need to teach this lesson?
The brief from the previous lesson, a comparison grid with a row per solution and the printable practice sheet linked at the end of this plan. Everything listed is either ordinary classroom equipment or a free printable from this site — there is nothing to buy and nothing to prepare beyond photocopying.
What mistakes should I expect in this lesson?
Three, each a reasoning error rather than carelessness: generates one solution and refines it; chooses the favourite and scores it kindly and keeps a solution that breaks a constraint. The plan gives the thinking behind each one and the teaching move that addresses the thinking rather than the symptom.
How do I know whether the lesson worked?
The exit ticket asks: “Three designs are compared. One meets every criterion but costs eight pounds against a five pound limit. What happens to it?.” It is ruled out, because it breaks a constraint however well it meets the criteria. Choosing it anyway means the constraint rule needs another run. That tells you whether the class needs a reteach or a thirty-second conversation before you plan tomorrow.
Is there a worksheet to go with Weighing Up Several Ideas?
Yes — 1 printable 3-5-ETS1-2 worksheet, linked at the end of the plan and free like the rest of the site. Each one comes with an answer key and 25 versions, so the practice after the lesson can be a different paper on every desk.
Is Weighing Up Several Ideas free to use?
Yes. The plan, its printables and their answer keys are free to read, print and photocopy for your own class, with no account and no email capture. It was last reviewed on 8 September 2026. Please do not resell it or republish it as your own.
Last reviewed 2026-09-08. Aligned to 3-5-ETS1-2 of the Next Generation Science Standards.