* Individual students: Some exceptionally gifted students might skip many grades, but there's no official record kept of the absolute maximum number of grades skipped by an individual. This information is also often kept private.
* School systems: Different school systems have different policies regarding grade skipping, making comparisons difficult. A school might have policies that allow skipping only one grade at a time, while others might allow for more.
* Definition of "skipped": Does "skipped" mean completely bypassing a grade level, or does it also include acceleration within a grade (e.g., taking advanced coursework)?
Therefore, there's no definitive answer to this question.