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Grading Infrastructure · The Last Mile

Clearing a Ten-Thousand-Submission Backlog Without Losing the Human Behind the Grade

The Last Mile brings coding, project management, and skilled trades education into carceral environments. As the program scaled, a two-person grading team hit a backlog no amount of manual reading could keep pace with. TDG built a grading platform that let those same two people scale the rote work, freeing them to focus on coaching and mentoring students, shipped as a working MVP over a single weekend while the backlog was still active.

The Last Mile grading platform
~10,000Submissions in the backlog at the start
2Grading modes, matched to the work
One WeekendFrom scoped three-month build to shipped MVP
100%Of grades finalized by a human before posting
The Opportunity

Two graders, a growing curriculum, and no room left to add hands.

The Last Mile brings coding, project management, and skilled trades education into carceral environments. As the program grew to cover more courses and more subjects, the team of two graders faced a backlog approaching ten thousand submissions, a volume the traditional model of every submission read and scored by a person was structurally incapable of keeping up with. Growth also meant asking specialized subject-matter experts to grade further outside their core expertise than before, since new courses were arriving faster than new specialist graders could be hired and trained.

TDG's read on the problem: adding more graders would have been bailing water out of a sinking ship. TLM didn't need more hands. It needed a new approach, one that let existing graders scale the rote work while freeing them up to help students in the ways that really matter, like coaching and mentoring.

Built Under Crisis, Not on a Roadmap

A three-month build, compressed into a weekend.

This was scoped as a three-month build. The severity of the backlog didn't allow for that timeline, so TDG compressed the plan into a single weekend and shipped a working MVP, built and deployed while the crisis was still active rather than after it had passed.

Our Approach

A grading system built around judgment, not just automation.

Coding assignments and open-ended writing don't grade the same way, so the platform doesn't force them through the same process. Deterministic mode builds a check-spec of code assertions directly from a tagged exemplar answer, built for work where a correct answer is checkable in code. LLM-graded mode scores against a weighted rubric of criteria that can run additive or diminishing, and pass/fail or scaled, built for work where judgment matters more than pattern matching.

A grader pastes in a submission and gets a scored result in seconds, with a rubric breakdown and a written narrative in the same feedback-sandwich style TLM's own graders already use. Every field is editable and nothing posts until a human confirms it. The score and the narrative are generated separately, with the score locked before the explanation is written, so the writeup can't quietly influence the number behind it.

The hardest grading calls aren't the perfect scores or the zeros. They're the middle bands, where the difference between a 2 and a 3 actually requires judgment, and where a grader without deep subject expertise needs the most support. Each question builds its own calibration bank across those bands, filling automatically from real graded submissions and regenerating a distilled profile of what separates each band as new examples land. When a grader overrides the AI's score, that correction is tagged and folded back into the bank, so the system learns from confirmed human judgment instead of unlabeled guesses.

Adding more graders would have been bailing water out of a sinking ship. TLM didn't need more hands. It needed a new approach to the problem.

— TDG's read on the problem
What's Next

Built into the tools TLM already runs.

The MVP TDG shipped over that first weekend is running today as a stopgap while TLM stands up its own infrastructure. The next phase, already designed, connects the platform directly to Canvas. Submissions sync into a queue automatically and match to the right question by ID, with anything that doesn't match flagged once for a manual link the system remembers from then on. Once a grade is finalized, it writes the score and feedback straight into Canvas SpeedGrader and posts a summary to the corresponding GitLab work item, so grading plugs directly into the systems TLM's ops team already uses instead of becoming a separate tool they have to check on its own.

Live

Deterministic & LLM-Graded Modes

Both modes live and in active use as TLM's stopgap grading system.

Live

Calibration Banking

Filling and regenerating automatically from every graded submission across the difficult middle bands.

Live

Full Audit Trail

Recorded for every finalized grade, including operator, model, and timestamp.

Designed, Ready to Build

Canvas Sync & SpeedGrader / GitLab Posting

Auto-matching and Finalize & Post to SpeedGrader and GitLab, ready to build as TLM migrates onto its own servers.

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