In educational evaluation field, we often have access to vertically equated scales. Scales means scores, measures, points. Vertically equated scores in the context of education are the ones that are comparable across grades, which means that you can pick a score from 5th grader and a score from 8th grader and consider them to be measuring the same construct on the same scale, such as math ability. I can say this or elaborate the concept in a couple of different ways.
- Vertically equated scales allow you to compare students of different grades on a common scale.
- If a 4th grader got a score of 50 and 9th grader also got score of 50, they have the same ability level.
- The 10 point difference among 5th graders (e.g., 50 and 60) and the 10 point difference among 8th graders (60 and 70) are considered equal.
Instead of providing a detailed methodological note, I'd like to use a metaphor to explain why equating is possible across different grades.