This is a working draft for Leslie's review. The dependency edges below are a first pass — the diagram and the prerequisite table are the parts to check hardest, since they drive hold-vs-advance decisions.
The course map shows the eight units as a spine — the crime scene first, the courtroom last. But the real prerequisite structure isn't a straight line: it's a directed graph. Forensic Science is more strictly cumulative than most subjects — fingerprint and impression comparison needs solid scene-and-evidence discipline, trace evidence leans on that same comparison skill, and DNA work needs both trace recovery and fluid identification. A weak skill early doesn't just lower one grade, it cascades into everything downstream that needs it. This page is the map a guide uses to find the concept that's actually blocking a stuck student.
An arrow means “must be mastered first.” Units 05, 06, and 08 each pull from two upstream units — those are the cascade points where one soft prerequisite quietly breaks several later units.
Prerequisite gating
A unit unlocks when its prerequisites are mastered — demonstrated, not merely seen. "Covered in class" is not the gate; a cleared rubric is. The difference matters most at the cascade points, where a soft prerequisite quietly breaks two or three later units.
| Unit | Must have mastered first |
|---|---|
| 01 Crime Scene & Evidence Basics | — (entry point) |
| 02 Fingerprints & Impression Evidence | 01 (scene documentation & evidence handling underpin every lift) |
| 03 Trace Evidence | 02 (class-vs-individual comparison carries over from impressions) |
| 04 Chromatography & Chemical Analysis | 02 (systematic side-by-side comparison discipline carries over) |
| 05 Blood & Bodily Fluids | 03 (trace-recovery technique) + 04 (chromatographic/chemical analysis) |
| 06 DNA & Biological Evidence | 03 (trace recovery) + 05 (biological-fluid identification) |
| 07 Ballistics & Toolmarks | 05 (spatter-angle & pattern reconstruction technique) |
| 08 The Case & the Courtroom | 06 (DNA interpretation & probability) + 07 (impression & trajectory evidence) |
Gap-cascade diagnosis
When a student stalls late, the visible symptom is rarely the real problem — the broken concept is usually upstream. Trace the arrows backward. Common cascades:
| Late symptom | Upstream concept to check first |
|---|---|
| Trajectory and toolmark reconstruction falls apart (Unit 07) | Spatter-angle & pattern analysis from Unit 05 — the reconstruction technique starts there. |
| DNA profiles won't interpret cleanly (Unit 06) | Trace-recovery technique from Unit 03 — a contaminated sample can't be read, not the DNA step itself. |
| The courtroom case won't hold together (Unit 08) | Converging evidence — the DNA interpretation from Unit 06 that the case is built on. |
| Blood and fluid identification goes wrong (Unit 05) | Where the sample came from — Unit 03 trace evidence collection. |
Using the graph to plan a re-attempt
The graph turns a "not yet" into a targeted re-attempt instead of a whole-unit re-teach. When a student fails a downstream demonstration:
- Trace backward to the upstream node the symptom points to.
- Re-attempt the upstream concept first — close the gap at its source, not where it surfaced.
- Then re-run the downstream demonstration. Often it passes without any re-teaching of the downstream unit at all, because the cascade is resolved.
This is also where the integration guide matters: some forensic science methods depend on an applied idea — statistics for match probability, proportional reasoning for scale and trajectory — from another spoke. When the upstream forensic science node looks solid but the student still stalls, check the cross-disciplinary dependency before re-teaching the forensic science.