Letter grades are hiding your child's actual math progress. Converting raw scores into A-through-F labels deletes nearly 70% of the useful information teachers and parents need to identify and fix specific learning gaps.
Converting raw math scores into letter grades wipes out nearly 70% of the diagnostic data, making it significantly harder for schools to identify which students actually need help. The resulting "letter-grade" profiles are highly unstable and can change drastically based on minor changes in the student population, meaning a child's grade may say more about the class average than their own mastery.
That "B" on the report card is a low-resolution snapshot of a high-resolution reality. It masks specific, fixable gaps in knowledge while making your child look identical to a peer who may have entirely different academic needs. If you rely solely on the letter, you are essentially flying blind when it comes to deciding where to provide extra support at home or through tutoring.
The stability of these grades is also a major concern. Because the system is so compressed, a child’s standing can fluctuate wildly based on how their peers perform. This means the feedback parents receive is often "noisy" and unreliable for long-term planning.
Schools prioritize letter grades because they simplify messy data into a clean transcript for administrators and colleges. However, researchers found this creates "Data Aphasia"—a state where the school system literally loses the ability to communicate nuanced student needs because the data has been flattened too far.
The study aimed to measure exactly how much "information entropy" (the ability to distinguish between different needs) is lost when we move from percentage scores to letters. They were looking for the "structural stability" of the data—basically asking if the grade stays meaningful if the student body changes slightly.
The move from percentages to letters creates "pseudo-homogeneity," where students with vastly different strengths and weaknesses appear identical on paper.
- The system deletes data. Converting scores to grades resulted in a 69% loss of diagnostic information.
- Compression is extreme. The grading system flattens data by a ratio of 19:1, effectively turning a detailed map of a child's mind into a single, blurry pixel.
- Reliability is a coin flip. While raw scores are 95% consistent in identifying a student's specific needs, letter grades drop that consistency as low as 62%.
- Small changes cause big swings. In the study, removing just one high-performing student from the group caused the number of identified student "types" to jump from four to eight. This suggests that a letter grade is often a reflection of the group dynamic rather than the individual's knowledge.
Letter grades are essentially "lossy" compression for human brains—like a blurry, low-quality photo of a complex painting. While they make administrative ranking easier, they are mathematically fragile.
The "Data Aphasia" the authors describe suggests that teachers themselves might lose the ability to see a student's specific struggle once that student is labeled a "C student." The label becomes a substitute for the reality, and the specific "why" behind the grade—whether it’s a struggle with fractions or a lack of focus during timed tests—is discarded.
This study is a preprint and has not yet undergone formal peer review. The findings are based on a mathematical simulation of 75 primary school students in a single subject (mathematics), which is a relatively small sample size. Because this was a "counterfactual" study rather than an observational one, it measures the mathematical behavior of the grading system rather than the qualitative ways teachers might use their own intuition to help students regardless of the grade.
- If your child receives a "B" or "C" in math, ask the teacher for the raw percentage scores or a competency breakdown (e.g., "How did they do on the multi-step word problems specifically?") rather than accepting the grade as a final verdict.
- If you are hiring a tutor based on a poor report card, do not just show them the grade; provide the actual graded tests or worksheets so they can see the specific errors the letter grade hides.
- If your child’s grade fluctuates from one term to the next, look at the raw scores to see if their performance actually changed, or if the "curve" or class average simply shifted.
- If the school uses relative grading (grading on a curve), ignore the letter grade for the purposes of academic intervention and focus exclusively on which concepts your child has actually mastered.
A letter grade is a tool for institutions to sort children, not a diagnostic tool for parents to help them. Stop treating the "A" or "B" as a complete picture and start asking for the raw data that shows exactly what your child knows—and what they don't.
Li Li, Yu Cao (2026). Data Aphasia: An Institutional Counterfactual Study of the Stability of Academic Cognition Under Letter-Grade Evaluation Systems. arXiv (preprint). — arxiv.org