Worked example · Design Technology · Year 9
DCF: Data and computational thinking → Data and information literacy
A secure Year 9 response, annotated against the success criteria. The matrix below is the only correct one, so you can mark from it. Totals out of 60: pine 50, plywood 46, oak 42, HDPE 39, MDF 36, acrylic 25. The idea worth stopping the class for is Step 5: MDF would fall apart in its first wet winter, yet no weighting on its own stops it scoring 60%.
| Material | Cost for one box | Cost score | Cost for 20 boxes |
|---|---|---|---|
| A. Pine | £3.20 | 4 | £64.00 |
| B. Oak | £9.60 | 1 | £192.00 |
| C. Exterior plywood | £4.10 | 4 | £82.00 |
| D. MDF | £2.40 | 5 | £48.00 |
| E. Recycled HDPE | £7.50 | 2 | £150.00 |
| F. Acrylic | £8.80 | 2 | £176.00 |
Every price is put in the right band, including the two just under a boundary (£4.10 and £8.80), and the 20-box costs are ready for the budget check later. Evidences criterion 1.
| Material | Durability × 3 | Welfare × 3 | Cost × 2 | Ease × 2 | Sustain. × 2 | Total /60 |
|---|---|---|---|---|---|---|
| A. Pine | 3 × 3 = 9 | 5 × 3 = 15 | 4 × 2 = 8 | 5 × 2 = 10 | 4 × 2 = 8 | 50 |
| B. Oak | 5 × 3 = 15 | 5 × 3 = 15 | 1 × 2 = 2 | 2 × 2 = 4 | 3 × 2 = 6 | 42 |
| C. Exterior plywood | 4 × 3 = 12 | 4 × 3 = 12 | 4 × 2 = 8 | 4 × 2 = 8 | 3 × 2 = 6 | 46 |
| D. MDF | 1 × 3 = 3 | 3 × 3 = 9 | 5 × 2 = 10 | 5 × 2 = 10 | 2 × 2 = 4 | 36 |
| E. Recycled HDPE | 5 × 3 = 15 | 2 × 3 = 6 | 2 × 2 = 4 | 3 × 2 = 6 | 4 × 2 = 8 | 39 |
| F. Acrylic | 4 × 3 = 12 | 1 × 3 = 3 | 2 × 2 = 4 | 2 × 2 = 4 | 1 × 2 = 2 | 25 |
Check: the six totals add up to 50 + 42 + 46 + 36 + 39 + 25 = 238. On a spreadsheet, =SUM(H2:H7) gives the same, so no row has been mistyped.
Every cell shows score × weight, so a wrong total can be traced to the cell that caused it, and the grand total is checked a second way. Evidences criterion 2.
| Rank | Material | Total | % of 60 |
|---|---|---|---|
| 1 | A. Pine | 50 | 83% |
| 2 | C. Exterior plywood | 46 | 77% |
| 3 | B. Oak | 42 | 70% |
| 4 | E. Recycled HDPE | 39 | 65% |
| 5 | D. MDF | 36 | 60% |
| 6 | F. Acrylic | 25 | 42% |
Correct order and percentages rounded sensibly (46 ÷ 60 = 76.7%, 25 ÷ 60 = 41.7%). Evidences criterion 2.
| Material | Old total | New total /70 | New rank |
|---|---|---|---|
| A. Pine | 50 | 50 + 8 = 58 | 1 |
| B. Oak | 42 | 42 + 2 = 44 | 4 |
| C. Exterior plywood | 46 | 46 + 8 = 54 | 2 |
| D. MDF | 36 | 36 + 10 = 46 | 3 |
| E. Recycled HDPE | 39 | 39 + 4 = 43 | 5 |
| F. Acrylic | 25 | 25 + 4 = 29 | 6 |
The winner did not change: pine is first with either set of weights, so that result is robust. But MDF jumped from 5th to 3rd, overtaking oak, just because the committee decided money mattered more. That worries me because nothing about MDF got better — it still turns to mush when wet. If cost had been weighted even higher, MDF could have come out on top, and the committee would have bought 20 boxes that fall apart before the second spring.
Uses the shortcut correctly, separates the robust result (the winner) from the fragile one (the order below it), and names the real-world consequence. Evidences criterion 3.
(a) £100 ÷ 20 = £5.00 per box at most. Oak (£192), recycled HDPE (£150) and acrylic (£176) are all over budget for 20 boxes, so they are out whatever they score. Oak came 3rd in the matrix, but the committee simply cannot buy it.
(b) The boxes will be outside all year through a wet Welsh winter, and MDF "swells and crumbles" once it gets wet. It scored 1 for durability, but its cheap price and easy cutting earned back enough points to reach 60%. A product that falls apart is not 60% successful; it has failed.
(c) Must-have rule: any material that scores 1 (unsuitable) for durability outdoors or for bird welfare is ruled out before the matrix is used. That removes MDF (durability 1) and acrylic (welfare 1). The budget removes oak, HDPE and acrylic. That leaves pine and exterior plywood, and pine wins between them, 50 to 46.
(d) Plywood costs £4.10 − £3.20 = £0.90 more, and 0.90 ÷ 3.20 = 0.28, so it is 28% dearer — yet both score 4. Banding throws away the size of the difference inside a band, and it can exaggerate differences at the edges: MDF at £2.40 scores a whole point more than pine at £3.20. The price is a fact anyone can check; the other four scores are the department's opinions, so two different teachers could score HDPE's welfare differently and change the result.
Spots that the budget and the fatal flaw are both "must-haves" that a weighted total cannot represent, writes a rule that could be applied by someone else, and separates the measured column from the judged ones with a calculation to back it. Evidences criteria 4 and 5.
I recommend 18 mm FSC pine for the 20 nest boxes. It scored 50 out of 60, the highest of the six, and it stayed first when the cost weight was doubled. Before scoring, I ruled out MDF and acrylic because each is unsuitable on durability or bird welfare, and oak, HDPE and acrylic are over the £100 budget. Twenty pine boxes cost £64, leaving £36. Pine's honest drawback is that it scored only 3 for durability and will weather outdoors, so I would spend part of the £36 on a water-based preservative for the outside of each box only — never inside, where the birds are.
Quotes the total, the robustness check, the rules that removed the others, the cost and the leftover budget, and deals with the weakness instead of hiding it. Evidences criterion 5.