Mr. S Teaches
Sign inRequest Tutoring
Menu
Sign inRequest Tutoring

Grade 7 · Science · 35 minutes

Unit 3 · Watersheds and Solutions · Lesson 2 of 2

Choose a Filter Without Overclaiming

Evaluate competing designs from multiple test measures and define a fair next test.

Mr. S Teaches · Original starter mini-lesson · MS7-SCI-06

Learning objective

Use a decision matrix to select a design meeting stated limits and identify an unmeasured outcome.

Before you begin

  • Read whole-number and decimal quantities.

Gather your materials

  • Paper or notebook
  • Pencil and the passage, model directions or data printed in this lesson

Language to know

filtrate
Material that has passed through a filter.
decision matrix
A table comparing options using the same criteria.
threshold
A minimum or maximum acceptable value.

Understand the concept

Paper design challenge: A model filter must cost at most 8 tokens, pass at least 40 mL per minute and reduce visible particles by at least 70%. Supplied test means: A costs 6, passes 55 mL/min and removes 60%; B costs 8, passes 45 and removes 80%; C costs 10, passes 30 and removes 95%. Each was tested with the same simulated input. Visible-particle removal is not a measure of bacteria or dissolved contaminants. No water in this activity is prepared for drinking.

Teach it step by step

  1. Read the challenge and copy all three limits before examining the results.
  2. Build a matrix and mark each design as passing or failing every limit.
  3. Explain why improving particle removal alone may make flow or cost worse.
  4. Recommend a design, then propose a fair repeat test and an outcome the existing evidence does not measure.

Make the thinking visible

Worked example or model response

B passes all limits: 8 is within budget, 45 is at least 40 and 80% exceeds 70%. A fails particle removal; C fails both budget and flow. B’s result supports the specified model task, not a drinking-water claim.

Guided practice

Together calculate the percentage-point gap between A’s result and the removal threshold. Discuss whether the gap can be ignored because A is inexpensive.

Independent practice

Propose a revision to A and list what must be retested. Then write a recommendation paragraph for B that acknowledges an unmeasured safety outcome.

Quick assessment

If B removes 80% of visible particles, can you conclude it removes 80% of dissolved substances?

Answer key & assessment criteria

Answers and teaching guidance

  1. Guided: A is 10 percentage points below the 70% minimum; cost does not cancel a failed requirement.
  2. Independent: Accept a plausible change with retests of flow, removal and cost. The recommendation should identify B and explain that microbes or dissolved substances were not tested.
  3. Quick check: No. Visible particles and dissolved substances are different measures; the result cannot be transferred without evidence.

Look for: Look for a claim that answers this lesson’s question, accurate use of the supplied evidence and an explanation of a limit or alternative. Ask the learner to point to the detail supporting each inference.

Make it work for your learner

More support

Use checkmarks and crosses in a prepared matrix; compare one requirement at a time.

Extension challenge

Assign uncertainty ranges to repeated test results and explain how B’s closeness to a threshold could affect confidence.

Selected contributions · Official sources

Standards connections

Selected NGSS band contribution; not complete performance expectation coverage.

Contributes to NGSS performance expectation

MS-ETS1-2

NGSS · Grades 6–8 band

Compare designs systematically against agreed criteria and constraints.

Read the official performance expectation ↗

This compares supplied design data systematically. It does not construct filters, test real water or establish removal of pathogens and dissolved materials.

Source and mapping checked 2026-11-04. This mini-lesson contributes selected skills; it does not claim full attainment.

Supporting Common Core literacy connection

RST.6-8.7

Common Core · Grades 6–8

Connect scientific prose with a diagram, model or table.

Read the official standard ↗

The provided scientific passage/model is explicitly analyzed in the activity. This selected literacy practice does not establish subject-content alignment or complete coverage of the standard.

Source and mapping checked 2026-11-04. This mini-lesson contributes selected skills; it does not claim full attainment.