Lesson plan Grade 6 Engineering & Design

Millbrook Creek Household Filter Design Challenge

Teams define a clarity target and a 20-credit budget, then design, build, and test a three-layer household water filter for the fictional town of Millbrook Creek.

Grade: Grade 6
Subject: Engineering & Design
Material: Lesson plan
Time: 50 min
Prep: Moderate prep
Materials: 2 clear plastic cups per team, 1 coffee filter or paper towel per team, 1 rubber band per team, About 1/4 cup each of gravel, sand, and cotton balls per team (shared from a class supply), 1 pitcher of muddy water per class (1 tablespoon of garden soil stirred into 1 quart of water), Measuring spoons, Measuring cup, 1 printed materials price card per team (listing each material's cost in build credits), 1 planning sheet per team, Index cards for the exit ticket

Standards

MS-ETS1-1 NGSS

Define the criteria and constraints of a design problem with sufficient precision to ensure a successful solution, taking into account relevant scientific principles and potential impacts on people and the natural environment that may limit possible solutions.

How this material aligns: Teams state a numeric clarity target and the exact 20-credit materials budget before building, defining the criteria and constraints this standard requires with real precision.

All materials for MS-ETS1-1 →

MS-ETS1-2 NGSS

Evaluate competing design solutions using a systematic process to determine how well they meet the criteria and constraints of the problem.

How this material aligns: Teams score their filter's output water against a shared 1-5 clarity rubric and compare it with another team's design, the systematic evaluation this standard names.

All materials for MS-ETS1-2 →

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This material is in the public domain (CC0) and may be copied, edited, and shared freely, without attribution. Updated 2026-07-16.

Objectives

Students will define a target clarity score and a 20-credit materials budget before designing a household water filter.
Students will build a layered filter from teacher-provided materials that stays within the stated budget.
Students will test their filter against muddy water and score its output using a shared clarity rubric.

Vocabulary

Filtration: Filtration is the step where water passes through layers of sand, gravel, or other materials that trap the small particles still left in it. It works like a very fine strainer.

Also: sediment, criteria, constraint, clarity

Teacher overview

The fictional town of Millbrook Creek has asked its middle school engineering class to design a low-cost household water filter that a family could build from hardware-store materials. Working in teams, students define exactly what "clean enough" means before they build anything, then test their design against muddy water and a fixed budget of 20 build credits, a system of fictional points assigned to each material. A common misconception in this lesson is that adding more layers automatically makes a filter better; the budget constraint forces teams to discover that extra layers can push a design over budget, or add cost without raising the clarity score enough to matter.

Procedure

Hook (5 min): Show students a cup of muddy water and ask how they would make it look clear enough to pour into a clean glass, without naming any materials yet. Collect two or three ideas on the board.

Direct instruction (10 min): Introduce the challenge: teams will design a layered filter using gravel, sand, cotton balls, and a coffee filter, each with a cost in build credits (gravel: 4 credits per scoop; sand: 3 credits per scoop; cotton: 2 credits per layer; coffee filter: 5 credits each). Every team has a 20-credit budget. Work through a sample recipe as a class: 2 scoops of gravel (2 x 4 = 8 credits), 1 scoop of sand (3 credits), 1 cotton layer (2 credits), and 1 coffee filter (5 credits) totals 8 + 3 + 2 + 5 = 18 credits, which fits the 20-credit budget with 2 credits left over. Explain the testing rubric: after filtering, teams score their output water's clarity from 1 (still cloudy) to 5 (clear enough to see through easily).

Design and budget planning (10 min): Teams first write the clarity score, from 1 to 5, that their filter must reach, then sketch their own layer order and combination on their planning sheet, listing each material's cost and totaling it to confirm they stay at or under 20 credits. Circulate and check each team's total before they proceed to building.

Build (10 min): Teams assemble their filter: stretch a coffee filter or paper towel over the mouth of one cup, secure it with a rubber band, and layer their chosen materials inside it in the order they planned, densest material on the bottom if they choose to include it.

Test and score (10 min): Each team pours a measured amount of muddy water into the second cup, slowly pours it through their filter into the first cup, observes the collected water, and scores its clarity from 1 to 5 using the rubric. Teams record their score and their total credit cost on the board. Ask the class whether adding more layers always makes a better filter, using the scores and costs on the board. Safety note: no one drinks or tastes the filtered water, because water that looks clear can still carry germs, and everyone washes their hands after handling the soil and muddy water.

Closure and exit ticket (5 min): Students answer individually on an index card: "A team's filter design costs 21 credits. Does it meet the 20-credit budget? By how many credits does it go over or stay under?" Collect and scan for the correct comparison before dismissal.

From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.

Answer Key

Answer: 18 credits. The sample recipe (2 scoops gravel at 4 credits each, 1 scoop sand at 3 credits, 1 cotton layer at 2 credits, 1 coffee filter at 5 credits) totals 8 + 3 + 2 + 5 = 18 credits, which is 2 credits under the 20-credit budget.
Exit ticket answer: Over by 1 credit. A design costing 21 credits exceeds the 20-credit budget by 21 minus 20, which is 1 credit, so it does not meet the constraint as designed.
Discussion answer: A filter can go over budget by adding too many layers, or it can waste credits on a layer that does not meaningfully raise the clarity score; both are reasons the budget and the clarity target must be checked together, not separately.

Differentiation

Support

Provide a partially completed planning sheet listing the four materials and their costs, and give struggling teams a pre-filled sample recipe (like the 18-credit example from direct instruction) as a starting point they can adjust rather than a blank sheet.

Extension

Challenge teams that finish early to design a second filter that costs at least 5 fewer credits than their first design while keeping the same clarity score, then explain in writing which single material swap made the biggest difference.

ELL supports

Pre-teach "filter," "layer," "clarity," and "budget" with a labeled diagram of a cup filter showing each layer named in English and, where possible, in students' home languages. Allow teams to record their design using labeled sketches with numbers instead of full sentences on the planning sheet.

Extensions

Invite a local water treatment operator, if available, to describe how a real treatment plant uses several stages, similar to the layers in this challenge, to clean water before it reaches homes, and have students compare their filter's layer order with the stages the visitor describes.