Graphic organizer Grade 4 Engineering & Design
A Reed Bed for Quillton Park Pond: A Design Decision Chain
A grade 4 six-box decision chain organizer tracing a fictional park board's choice of a planted reed bed over a settling box or a chemical feeder, with an exemplar.
Objectives
- Students will trace a design decision from the problem through the choice in six linked boxes.
- Students will sort a park board's rules into goals and limits.
- Students will explain why a fix that uses living plants was chosen over two other fixes.
Vocabulary
Key words: reed bed, criteria, constraint, roots, settling box
Teacher overview
This organizer is a six-box decision chain read from the top down, with an arrow between each box and the next, so the finished page shows how a park board got from a green pond to one chosen fix. A short evidence table sits beside box 4 and holds what the board learned about each option. Fourth graders often treat a design choice as a vote about which idea sounds nicest, which is why box 3 is filled in before the options appear and why box 5 asks for the reason rather than the winner alone. The living-plant option is worth pausing on: the cleaning is done by the roots and by the tiny living things growing on them, not by the gravel alone.
Organizer
Read the board notes. Then fill in the chain from the top down.
Notes from the Quillton Park board, in the town of Quillton
Every August the duck pond turns green and smells bad. A ditch carries water into the pond. The ditch collects rain from the parking lot and from the big lawn. The lawn is fed twice a year to keep the grass thick. Rain washes some of that lawn feed into the ditch. Extra plant food in the water lets green scum grow fast on the pond.
The board wrote four rules for a fix. It must take plant food out of the ditch water before the water reaches the pond. It must be safe for ducks and for children. It must run on its own, because no worker is at the park between monthly visits. It must fit in a strip of ground 40 feet long.
The board looked at three fixes.
Fix 1 is a concrete settling box 10 feet long. Grit and sand drop to the bottom of the box. A truck must pump the box out twice a year. The box does not take plant food out of the water.
Fix 2 is a reed bed. It is a shallow gravel channel 30 feet long, planted with cattails and rushes. Water trickles slowly through the gravel. Roots and the tiny living things coating them take in plant food and hold back dirt. A crew cuts the plants back once each year. The bed needs one growing season before it works well.
Fix 3 is a chemical feeder. It sits on a post beside the ditch and drips a clearing chemical into the water. It works the same day it is switched on. A trained worker must check it weekly and keep the supply locked up.
Decision chain
| Box | What belongs in this box | Your answer |
|---|---|---|
| 1 | The problem: what happens to the pond, and when | |
| ↓ 2 | The cause: where the extra plant food comes from | |
| ↓ 3 | The rules: two things the fix must do, and two limits it must stay inside | |
| ↓ 4 | The options: name the three fixes the board looked at | |
| ↓ 5 | The choice and the reason: which fix, and which rules the other two broke | |
| ↓ 6 | What to watch: one thing to check after the fix is built |
Evidence table for box 4
| Fix | Takes plant food out? | Safe for ducks and children? | Runs on its own? | Fits in 40 feet? | How soon it works |
|---|---|---|---|---|---|
| 1: settling box | |||||
| 2: reed bed | |||||
| 3: chemical feeder |
From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.
Completed Exemplar
Decision chain
| Box | What belongs in this box | Your answer |
|---|---|---|
| 1 | The problem: what happens to the pond, and when | Every August the duck pond turns green and smells bad. |
| ↓ 2 | The cause: where the extra plant food comes from | The lawn is fed twice a year. Rain washes some of that lawn feed down the ditch and into the pond, and the extra plant food lets green scum grow fast. |
| ↓ 3 | The rules: two things the fix must do, and two limits it must stay inside | Must do: take plant food out of the ditch water, and be safe for ducks and children. Limits: it has to run on its own between monthly visits, and it has to fit in a strip 40 feet long. |
| ↓ 4 | The options: name the three fixes the board looked at | A concrete settling box, a planted reed bed, and a chemical feeder. |
| ↓ 5 | The choice and the reason: which fix, and which rules the other two broke | The reed bed. It is the only fix that takes plant food out, stays safe for ducks and children, runs on its own, and fits in the strip. The settling box only catches grit, so it misses the first rule. The chemical feeder needs a trained worker every week, so it breaks the runs-on-its-own rule. |
| ↓ 6 | What to watch: one thing to check after the fix is built | Check next August whether the pond still turns green, and check that the cattails and rushes are growing in well during the first season. |
Evidence table for box 4
| Fix | Takes plant food out? | Safe for ducks and children? | Runs on its own? | Fits in 40 feet? | How soon it works |
|---|---|---|---|---|---|
| 1: settling box | no, it only catches grit and sand | yes | yes, a truck pumps it out only twice a year | yes, it is 10 feet long | right away |
| 2: reed bed | yes, roots and the life on them take it in | yes | yes, a crew only cuts it back once a year | yes, it is 30 feet long | after one growing season |
| 3: chemical feeder | yes | only with the supply locked up | no, a trained worker checks it weekly | yes, it sits on a post beside the ditch | the same day |
Differentiation
Support
Read the board notes aloud twice, pausing after each fix so students can underline the sentence that answers one evidence column. Fill boxes 1 and 6 as a class and leave boxes 2 through 5 for student work. Accept short phrases instead of sentences in the evidence table, and allow students to copy wording straight from the notes.
Extension
Ask students to write a seventh box for what the board should do if the reed bed still lets green scum through after two summers. They should name one change to the bed itself, such as making it longer or adding a second row of plants, and one change away from the bed, such as feeding the lawn less often, then say which change they would try first and why.
ELL supports
Pre-teach ditch, scum, gravel, cattail, and trickle with photographs or quick sketches, and show the reed bed idea with a tray of gravel, a small plant, and a cup of water poured slowly through. Provide the sentence frames "The pond turns green because ____." and "Fix ____ was not chosen because ____." Accept labeled drawings in boxes 1 and 2.
Extensions
Walk students out, with adult supervision and everyone staying well back from the water's edge, to the nearest pond, ditch, or rain garden on school grounds and build a one-box addition to the chain for what they can actually see entering the water there. Ask what the class would have to measure over a year to know whether a planted strip is working, and compare that list with the single line the class wrote in box 6.