Cover lesson · Design Technology · Year 9 · Intermediate

Choosing materials with a weighted matrix

DCF: Data and computational thinking → Data and information literacy

Name: Class: Date:

Cover teacher — you need no subject knowledge

Print: this sheet, one per pupil, and the stimulus sheet "Nest box materials: the brief and the data", one between two. No computers are needed; the same data is in nest-box-material-scores.csv if you are in a computer room. Calculators help but are not essential — every sum is small.

Run: 5 min read the brief and the six materials · 5 min Step 1, cost scores · 15 min Step 2, the weighted matrix · 5 min Step 3, ranking · 8 min Step 4, change a weight · 10 min Step 5, what the totals hide · 7 min Step 6, the recommendation.

Collect: this sheet. The full matrix and every total are on the worked example sheet. The one number to check first: pine scores 50 out of 60 and wins; the Pine row is already filled in below as a model.

What you are doing

Designers rarely find a material that is best at everything. A weighted matrix turns a choice into data: score each option against each criterion, multiply by how much that criterion matters, and add up. You will use one to choose a material for 20 school nest boxes — and then test whether the matrix can be trusted, because a single total can hide a problem that should rule a material out altogether.

Step 1 — turn prices into cost scores

Use the price bands on the stimulus sheet. A cheaper material gets a higher score.

Material	Cost for one box	Cost score	Cost for 20 boxes
A. Pine	£3.20	4	£64.00
B. Oak	£9.60
C. Exterior plywood	£4.10
D. MDF	£2.40
E. Recycled HDPE	£7.50
F. Acrylic	£8.80

Step 2 — the weighted matrix

In each box write score × weight. Take the four judgement scores from the stimulus sheet and the cost score from Step 1. Then add across for the total.

Material	Durability × 3	Bird welfare × 3	Cost × 2	Ease of making × 2	Sustainability × 2	Total out of 60
A. Pine	3 × 3 = 9	5 × 3 = 15	4 × 2 = 8	5 × 2 = 10	4 × 2 = 8	50
B. Oak
C. Exterior plywood
D. MDF
E. Recycled HDPE
F. Acrylic

Step 3 — rank them

List the six materials from highest total to lowest, and write each total as a percentage of 60. Pine: 50 ÷ 60 = 83%.

Rank	Material	Total	% of 60
1
2
3
4
5
6

Step 4 — change one weight

The head teacher says money is tight and asks the committee to change the cost weight from × 2 to × 4. Nothing else changes. The highest possible total is now 14 × 5 = 70.

Shortcut: each new total = old total + (cost score × 2).

Material	Old total	New total (out of 70)	New rank
A. Pine	50
B. Oak
C. Exterior plywood
D. MDF
E. Recycled HDPE
F. Acrylic

Did the winner change? Which material moved the most, and why does that worry you?

Step 5 — what the totals hide

(a) The committee has £100 for 20 boxes. What is the most they can spend per box? Using your Step 1 table, which materials are over budget whatever their score?

(b) MDF scored 60% overall. Read its description on the stimulus sheet. Why should MDF never have been scored at all for this product?

(c) Write a must-have rule that the committee should apply before scoring, so that a material with a fatal flaw is ruled out instead of being rescued by its other scores. Which materials does your rule, plus the budget, leave?

(d) The price column is measured data; the other four scores are judgements. Pine (£3.20) and plywood (£4.10) get the same cost score. By what percentage is plywood dearer than pine? What does turning prices into bands throw away?

Step 6 — your recommendation to the eco-committee

Four or five sentences. Name the material, quote its total, say what the must-have rule and the budget ruled out, give the cost for 20 boxes, and state one honest drawback of your choice and what you will do about it.

Step by step

5 min — Read the brief and the six material descriptions on the stimulus sheet.
5 min — Step 1: cost scores, and the cost of 20 boxes of each.
15 min — Step 2: fill in the matrix. On a computer, open nest-box-material-scores.csv, add a cost score column with =IF(B2<3,5,IF(B2<5,4,IF(B2<7,3,IF(B2<9,2,1)))), then a total with =C2*3+D2*3+G2*2+E2*2+F2*2.
5 min — Step 3: rank the six and work out percentages.
8 min — Step 4: change the cost weight and re-rank.
10 min — Step 5: the budget, the must-have rule, measured data and judgements.
7 min — Step 6: write the recommendation.

Success criteria

I can convert measured data (prices) into scores using a stated rule.
I can complete a weighted matrix accurately, showing score × weight in every cell.
I can test whether a result depends on the weights by changing one and re-ranking.
I can explain why a high total can hide a fatal flaw, and write a must-have rule that fixes it.
I can tell measured data from judgement, and write a recommendation that quotes numbers and admits a drawback.

If you finish early

The committee wants the boxes to last as long as possible. Keep every other weight as it was and raise the durability weight one step at a time. At what durability weight does plywood first beat pine?
Re-score oak for "ease of making" if the school had a CNC router to cut the parts. Does oak now win? Does it matter, given the budget?
Design your own weighted matrix for choosing a material for a phone stand. Choose four criteria, justify each weight in one sentence, and say which criterion would be a must-have.