Project Grade 6 Math

Vexford Street Rain Garden: A Grade 6 Design Proposal

A four-session grade 6 project where students size a rain garden with fractional depths, keep it inside a budget, and propose it to a public works committee.

Grade: Grade 6
Subject: Math
Material: Project
Time: 4 sessions, ~180 min total
Prep: Moderate prep
Materials: Tape measures, Graph paper, Rulers, Calculators

Standards

6.G.A.2 Common Core Math

Find the volume of a right rectangular prism with fractional edge lengths by packing it with unit cubes of the appropriate unit fraction edge lengths, and apply the formulas V = l w h and V = b h to find volumes of right rectangular prisms with fractional edge lengths in the context of solving real-world and mathematical problems.

How this material aligns: In milestone 2 students apply the volume formula to a rain garden whose ponding depth is a fraction of a foot, such as three quarters of a foot.

All materials for 6.G.A.2 →

6.RP.A.3 Common Core Math

Use ratio and rate reasoning to solve real-world and mathematical problems, e.g., by reasoning about tables of equivalent ratios, tape diagrams, double number line diagrams, or equations, including finding a percent of a quantity and converting measurement units.

How this material aligns: Milestone 1 converts inches of rain on a stated roof area into gallons, and milestone 3 checks the cost per square foot against a fixed budget.

All materials for 6.RP.A.3 →

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This material is in the public domain (CC0) and may be copied, edited, and shared freely, without attribution. Updated 2026-09-23.

Objectives

Students will convert rainfall on a roof area into gallons and cubic feet of runoff.
Students will apply the volume formula to a basin whose depth is a fraction of a foot.
Students will compare two designs against a stated budget and recommend one.

Vocabulary

Rain garden: A rain garden is a shallow planted dip in the ground that catches rain running off a roof or driveway and lets it soak slowly into the soil. Its deep-rooted plants help clean the water.

Also: runoff, ponding depth, volume, budget

Teacher overview

A rain garden is a shallow planted basin that holds roof and pavement runoff long enough for it to soak into the ground instead of rushing to a storm drain. In this project, students design one for the fictional Eastridge Middle School, where the bus canopy roof drains straight onto Vexford Street, and they must fit their design inside a stated strip of ground, a stated range of ponding depths, and a stated budget. Teams turn in a written proposal with a scale drawing and a cost sheet, addressed to the fictional Eastridge Public Works Committee, and they present it in the final session.

Vexford Street Rain Garden: A Grade 6 Design Proposal — Grade 6 Math

Name: ____________________________ Date: ______________

Project Brief

The driving question. How large, and how deep, does a rain garden have to be to hold the runoff from one storm, and can it be built for the money the committee has?

The client. The fictional Eastridge Public Works Committee has asked your team for a proposal. The committee will fund one design.

The site. Rain falling on the school's bus canopy runs off a roof of 4,000 square feet. The only open ground is a strip along Vexford Street that measures 40 feet by 15 feet.

The constraints. Your design must meet all five.

The garden must fit inside the 40-foot by 15-foot strip, so its area can be at most 600 square feet.
The ponding depth must be at least 1/2 foot and no more than 1 1/2 feet, because deeper basins keep water standing too long and can be unsafe, and shallower ones hold too little water for their area.
The garden must hold all of the runoff from a storm that drops 1 inch of rain on the 4,000-square-foot roof.
Soil, stone, and plants cost 4 dollars for each square foot of garden, and the committee has 2,000 dollars.
The ponding depth you choose must be written as a fraction or a mixed number of a foot, not as a decimal.

Useful figures. One inch of rain on one square foot of roof gives 0.623 gallons of runoff. That is all of the rain falling on the roof; a real roof sends somewhat less to the garden, so planning for the full amount leaves a margin of safety. One cubic foot holds 7.48 gallons.

The deliverable. Each team turns in a written proposal of one to two pages, a scale drawing of the garden on graph paper, and a cost sheet. The proposal must state the runoff in gallons, the garden's length, width, and ponding depth, the volume it holds in cubic feet and in gallons, the total cost, and one sentence saying why the team chose this design over the other one it tested.

Milestones

Session 1: Find the runoff. Measure a roof's outline from the ground or a marked rectangle on the school grounds with tape measures to practice, then work with the 4,000-square-foot roof given in the brief. Find the gallons of runoff from a 1-inch storm, then convert that number to cubic feet. Output: a one-page runoff sheet showing both numbers and the steps used.

Session 2: Size the garden. Choose a length, a width, and a ponding depth that meet constraints 1, 2, and 5. Use the volume formula to find how many cubic feet your basin holds, then convert to gallons and compare with session 1. Test a second design with a different depth. Output: a sizing table comparing the two designs, with a check mark beside each one that holds the storm.

Session 3: Price the designs. Multiply the area of each design by the cost for each square foot, and compare both totals with the committee's budget. Cross out any design that fails the budget or the storm. Draw the chosen garden to scale on graph paper, label its length, width, and ponding depth, and write the proposal. Output: a cost sheet for both designs, with the recommended one circled, and a draft of the proposal and scale drawing.

Session 4: Propose and present. Present for four minutes to the class acting as the fictional committee, and answer two questions from the audience. Output: the proposal, the scale drawing, and the cost sheet, turned in together.

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

Rubric

Score each criterion on four levels.

Runoff calculation

Level 4: The runoff is correct in both gallons and cubic feet, every step is shown, and units are labeled throughout.
Level 3: The runoff is correct in both units, with minor gaps in the shown work.
Level 2: One of the two conversions is correct, or the work is correct but unlabeled.
Level 1: Neither conversion is correct, or the roof area was not used.

Sizing and volume

Level 4: Two designs are tested, both use a fractional ponding depth inside the stated range, and the volume of each is computed correctly and compared with the storm.
Level 3: Two designs are tested and volumes are correct, with one constraint checked loosely.
Level 2: Only one design is tested, or a volume is computed with a depth outside the stated range.
Level 1: Volume is not computed, or the garden does not fit the strip.

Budget within the constraint

Level 4: Both designs are priced correctly, the recommendation stays within the budget, and the team explains the trade-off between area and depth.
Level 3: Both designs are priced correctly and the recommendation stays within the budget.
Level 2: Pricing has an arithmetic error, or the recommended design exceeds the budget by a small amount.
Level 1: Costs are missing, or the recommended design is far over the budget.

Proposal and scale drawing

Level 4: The proposal states every required number, the drawing is to a stated scale with all three dimensions labeled, and the closing sentence gives a clear reason for the choice.
Level 3: The proposal states every required number and the drawing is labeled, with a scale that is stated but applied unevenly.
Level 2: The proposal is missing one required number, or the drawing has no stated scale.
Level 1: The proposal is missing several required numbers, or no drawing is turned in.

Differentiation

Support

Give these students the runoff for the fictional school already computed in gallons, so session 1 becomes the conversion to cubic feet alone. Offer a sizing table for the fictional site with the length fixed at 40 feet and only the width and depth left to choose, and allow a depth of 1/2 foot or 1 foot rather than any fraction.

Extension

Ask these students to test whether their design for the fictional school would also hold a storm that drops 1 1/2 inches of rain, and to state the smallest ponding depth that would work at their chosen area. They should add a short paragraph explaining whether the deeper design still meets constraints 2 and 4, and why its cost under the committee's pricing does or does not change.

ELL supports

Pre-teach runoff, ponding depth, volume, and budget with a labeled cross-section drawing of a rain garden beside a roof and a downspout. Provide these sentence frames for the proposal: "The storm sends ___ gallons off the roof." and "Our garden is ___ feet long, ___ feet wide, and ___ of a foot deep, so it holds ___ cubic feet."

Extensions

Invite the school's facilities staff to hear the final presentations and to say what would actually be involved in digging on the site, such as buried utilities, mowing access, and who would weed the garden in August. Adding those practical limits to the students' cost sheets shows the class that a design that satisfies the arithmetic still has to satisfy the people who will maintain it.