Water for Schools
Menu

Graphic organizer Grade 6 Engineering & Design

Criteria and Constraints for the Ravelle Hollow Fire Cistern

A grade 6 sorting frame that splits eight statements about a fictional buried fire cistern into criteria, constraints, and wants, each with a stated test and target.

Objectives

  1. Students will sort eight client statements into criteria, constraints, and wants.
  2. Students will write a measurable test and target for each criterion and constraint.
  3. Students will explain why a want cannot be scored the way a criterion can.

Vocabulary

Cistern
A large tank that stores rainwater collected from a roof so it can be used later, usually for watering plants.

Also: criterion, constraint, suction lift, measurable target

Teacher overview

This organizer is a three-column sorting frame. Students take eight statements collected from a fictional client, decide whether each one is a criterion, a constraint, or only a want, and then write the test and target that would tell an engineer whether the finished design satisfies it. The setting is Ravelle Hollow, an invented village with no water mains, and every number in the brief was made up for the exercise. The misconception to plan for is common at this grade: students treat criteria and constraints as the same thing because both sound like requirements. A criterion is a goal the design is measured against and can meet well or poorly, while a constraint is a hard boundary the design either stays inside or does not. Students also tend to accept vague statements such as "the water should be clean," so the third column, which forces a test and a number, does most of the teaching here.

Criteria and Constraints for the Ravelle Hollow Fire Cistern — Grade 6 Engineering & Design
Name: ____________________________ Date: ______________

Organizer

Ravelle Hollow is a fictional village of about forty houses with no water mains and no hydrants. The fire company wants a buried tank, called a cistern, that a pumper truck can draw from. Eight people gave the design team a statement. Sort each one, then write how you would test it.

Statements from the client

  1. The cistern must supply 250 gallons per minute for 30 minutes to fight one house fire.
  2. The truck pump cannot lift water more than 18 feet, so the water surface must sit within that distance below the pump.
  3. The lid must hold a loaded fire truck driving over it.
  4. The village has set aside $40,000 and cannot spend more.
  5. The cistern should refill within 3 days after it is emptied.
  6. Neighbors would like the site to look tidy from the road.
  7. State rules keep any buried tank at least 50 feet from a septic drainfield.
  8. The water should stay cool and dark so that algae does not grow in it.

Sorting frame

Statement Criterion, constraint, or want? Test and target: how would you measure it?
1. Supplies 250 gallons per minute for 30 minutes
2. Water within 18 feet of the pump
3. Lid holds a fire truck
4. Costs $40,000 or less
5. Refills within 3 days
6. Site looks tidy
7. At least 50 feet from the drainfield
8. Water stays cool and dark

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

Completed Exemplar
Statement Criterion, constraint, or want? Test and target: how would you measure it?
1. Supplies 250 gallons per minute for 30 minutes Criterion Multiply the flow by the time. The stored volume must be 7,500 gallons or more, which a tank chart confirms.
2. Water within 18 feet of the pump Constraint Measure from the truck's pump to the lowest water level in the tank. The reading must be 18 feet or less.
3. Lid holds a fire truck Constraint Ask the supplier for the lid's rated load and compare it with the weight of the village pumper. The rating must be the larger number.
4. Costs $40,000 or less Constraint Add the quoted prices for the tank, the digging, and the fill pipe. The total must not pass $40,000.
5. Refills within 3 days Criterion Empty the tank once, then read the depth gauge each day. The tank must be full again by day 3.
6. Site looks tidy Want There is no number to measure, so the team records it as a preference and settles it by asking the neighbors to pick among finished designs.
7. At least 50 feet from the drainfield Constraint Measure on the site plan from the tank wall to the nearest drainfield line. The distance must be 50 feet or more.
8. Water stays cool and dark Criterion Use a buried tank with a sealed lid, then record the water temperature monthly and check for green growth. Cooler and clearer readings score better.

Statements 1, 3, and 5 can reasonably be sorted either way. Accept either label when the student's reason uses the definitions of criterion and constraint above.

Differentiation

Support

Hand these students a frame with statements 1 and 6 already sorted and explained, since those two show the clearest contrast between a criterion and a want. Provide a word bank of test verbs: measure, weigh, count, time, compare.

Extension

Have students rank the four constraints from hardest to easiest to satisfy and write one sentence on which constraint they would ask the village to relax first, along with what the design team would gain by relaxing it.

ELL supports

Post a two-line definition card for criterion and constraint with a simple example from outside water, such as a backpack that must weigh under a set limit compared with a backpack that should carry as many books as possible. Allow the third column to be answered with a sentence frame: "Measure the ____ and check that it is ____ than ____."