Year 4 · 60 minutes · Evaluation
When is asking a person better than choosing a bin?
Our sorter uses a synthetic material score. Scores for two material types overlap, so no single threshold separates every item correctly. A reject zone sends uncertain items to a person. This can reduce wrong-bin decisions while increasing review work. These values are invented measurements, not real recycling advice or calibrated probabilities.
Print the fixed set of material scores and labels. Use two containers and a review tray. Explain that actual recycling rules depend on local facilities; the invented materials are called A and B.
Count missed targets separately from false alarms. Useful earlier investigations: y3-gate Use pairs with predictor/operator roles. Swap after the first comparison. Each learner draws or writes their own explanation using one exact case.
Australian Curriculum Version 9 · Digital Technologies: AC9TDI4P02, AC9TDI4P05. Selected aspects only. This activity contributes evidence; it does not cover the full descriptor or achievement standard. A programming descriptor is not claimed for merely moving controls. ACARA AI curriculum connection · V9 Technologies These are planning connections, not ACARA endorsement or exhaustive descriptor alignment.
Sort paper items with a threshold at 50. Turn over reference labels and identify errors.
Ask: “Is there a gap between all A and all B scores?”
Listen for: “No; they overlap.”
Record how a wider review band might affect wrong bins and workload.
Ask: “Could fewer automatic mistakes require more human work?”
Listen for: “Yes, more items might be reviewed.”
Adjust threshold with reject width fixed, then width with threshold fixed. Record both counts for three settings.
Ask: “Which items moved from a wrong bin into review?”
Listen for: “Those near the boundary.”
Inspect a confidently wrong item far from the overlap.
Ask: “Will a narrow reject zone catch this one?”
Listen for: “No, it is far from the line.”
Choose a setting under a review capacity of four items per batch. Label unresolved errors and design a clear review message.
Ask: “Can you meet the review budget without hiding mistakes?”
Listen for: “We need to show both counts, even if some errors remain.”
Partners exchange settings and reproduce counts.
Ask: “What could make your threshold unsuitable elsewhere?”
Listen for: “Different materials or different score measurements.”
One threshold can remove all errors.
Widen the reject zone with scores and threshold fixed. Predict the direction of wrong-bin and review counts.
A labelled outlier far from the boundary is confidently mis-sorted and bypasses a narrow reject zone.
Meet a four-item review capacity while documenting remaining wrong-bin decisions and a usable review message.
Check that reviewed items are not quietly counted as correct automatic predictions. Ask learners to locate one error excluded from review.
Work with eight score cards and count outcomes physically before using the full batch.
Assign different costs to contaminating each bin and compare the preferred policy with the accuracy-only choice.
A recycling gate policy with a three-outcome audit and review instructions.
Synthetic A/B materials only. Do not handle waste or apply this threshold to real recycling decisions.
Sweep classification thresholds over a large fixed synthetic batch. Change the review width and compare automatic-error and review-work curves.
| Criterion | Beginning | Secure | Extending |
|---|---|---|---|
| Error accounting | Combines review and correct outcomes | Separates mistakes, correct decisions and review | Explains which cases each measure hides |
| Design justification | Chooses a threshold by appearance | Uses counts and review capacity | Documents a residual outlier and a monitoring need |
Australian Curriculum Version 9 · Digital Technologies
References: AC9TDI4P02, AC9TDI4P05. Read the current source (checked 2026-09-07).
Evidence to assess: A recycling gate policy with a three-outcome audit and review instructions.
Selected aspects only. This activity contributes evidence; it does not cover the full descriptor or achievement standard. A programming descriptor is not claimed for merely moving controls. Moderate the supplied illustrative responses against your school unit and current achievement standard.
These are planning estimates to test with your class. A short session develops one supported claim; it does not compress the whole senior project.
| Stage | 45 minute focus | 60 minute investigation |
|---|---|---|
| Readiness and prediction | 0–5 | 0–5 |
| Trace the supplied example | 5–13 | 5–15 |
| Author and run cases | 13–25 | 15–35 |
| Counterexample and redesign | 25–35 | 35–45 |
| Explain and discuss | 35–42 | 45–55 |
| Export and handover | 42–45 | 55–60 |
For a longer project, use three 50-minute sessions. Session 1 (0–50): readiness, model, hypothesis and initial cases. Export a project and record the next test. Session 2 (50–100): reopen, check settings, author counterexamples and revise the design. Export the changed project and identify unresolved evidence. Session 3 (100–150): independent peer test, final artefact, individual explanation and moderation. If using two 60-minute sessions, stop at minute 60 after saving the first comparison; use 60–120 for redesign, independent test and defence.
Entry check: Count missed targets separately from false alarms. Ask the learner to demonstrate it before choosing the level of support.
Preparation: allow about 15 minutes to run the starter, print the cards and check a project can be reopened. This estimate has not yet been measured in a classroom pilot.
Read the entry question aloud, model one row, and label the units. Offer the case table as a large-print sheet. Keep mathematical derivations optional until the learner can explain the comparison.
For one device, use a projector: one pair predicts, one operates, and the class records on paper. Swap roles after the first comparison. For individual access, support keyboard controls and a written table equivalent to each visual. Learners may explain orally or with an annotated diagram. Never require personal data, a recorded voice, or a photograph.
Mixed readiness: if the entry check is difficult, use the linked prerequisite and the first two case cards; retain the same central question. If secure, ask the learner to design an unseen test and state which explanation it could disprove.
Classify scores at or above the boundary as positive. Compare each decision with its known label.
Starting parameters: Boundary = 0.5
TP 2; FP 1; FN 1; TN 1.
| case | score | actual | predicted | outcome | cost |
|---|---|---|---|---|---|
| 1 | 0.2 | False | False | TN | 0 |
| 2 | 0.48 | True | False | FN | 0 |
| 3 | 0.51 | False | True | FP | 0 |
| 4 | 0.8 | True | True | TP | 0 |
| 5 | 0.9 | True | True | TP | 0 |
These are authored examples, not work collected from children. Assess reasoning using the lesson rubric, not whether the first prediction was correct.
Beginning: “It worked because the result looks right.” This identifies no exact case, control or measurement. Ask the learner to point to one row and say what happened.
Developing: “In the first case I recorded case: 1; score: 0.2; actual: False; predicted: False; outcome: TN; cost: 0.” This cites evidence, but does not yet explain how the result follows from the rule. Ask the learner to trace the relevant step.
Secure: “For the first supplied case, case: 1; score: 0.2; actual: False; predicted: False; outcome: TN; cost: 0. I can trace it using this mechanism: Classify scores at or above the boundary as positive. Compare each decision with its known label. My result supports a claim about these supplied cases. It does not establish that the same result holds outside them.” Look for an accurate trace, the actual settings and a bounded claim; accept equivalent oral or visual evidence.
Extending: The learner constructs and reruns a new case, reports whether the first explanation survives, and defends a revised design. Use this concrete challenge: Create an awkward object near the boundary. Compare two rules and name the mistake each accepts. Require the original and changed evidence and this boundary: Scores and objects are synthetic; a threshold cannot remove overlapping groups.
Moderation: first assess independently against each lesson criterion. Compare the exact trace or artefact that led to your judgement. Resolve differences using evidence, not polished language. Keep each learner's individual explanation even when the artefact was produced in a group.