* Ordinal: If the test scores represent ranks (e.g., 1st, 2nd, 3rd place), then it's ordinal. The differences between ranks aren't necessarily equal.
* Interval: If the test scores represent a scale with equal intervals between points (e.g., 80, 85, 90), then it's interval. The difference between 80 and 85 is the same as the difference between 90 and 95. However, there's no true zero point (a score of 0 doesn't necessarily mean the absence of knowledge).
A categorical variable would involve assigning individuals to categories (e.g., pass/fail, high/medium/low). While you could *categorize* test scores (e.g., creating grade bands A, B, C, etc.), the underlying score itself is not categorical.