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The Math of Success: Understanding Our Percentile Grading Engine

Keywords: Percentile Rank Formula, Diagnostic ID, Grading Logic, IB Biology Grade Boundaries.

How do we turn a raw string of correct answers into a Grade 1–7? It’s not a simple percentage. It’s a sophisticated Percentile-Based Grading Engine. Here’s a look under the hood at how we calculate your standing.

The Logic of the Rank

When you submit a Diagnostic Test, the system isolates every First Attempt associated with that specific diagnostic_id. We ignore second or third attempts to ensure the "Anti-Skew Lock" remains intact.

We then apply the Percentile Rank formula:

• L: The number of students who scored lower than you.
• S: The number of students who achieved the same score as you.
• N: The total number of unique students in the cohort.

Mapping to the IB 1–7 Scale

Once your percentile (P) is calculated, the system maps it against our Admin Grade Boundaries.

Unlike a fixed school test where 90% is always an A, our boundaries reflect the difficulty of the specific paper.

If a paper is notoriously difficult and the top student scores only 60%, that student still lands in the 99th percentile and receives a Grade 7. This mimics the "curve" or "moderation" process used by international exam boards.

Why Authentication is Required

Because these diagnostics rely on unique data points, guest access is disabled.

Your Results History dashboard acts as your personal academic log, tracking your Raw Percentage vs. your Percentile Grade over time.

If your raw score stays the same but your percentile rises, it means you’re mastering the harder topics that are tripping up your peers.