Freshman to senior is about eight inches
A boy who opens freshman year at 5'2" and finishes senior year at 5'10" has followed a completely normal path. The biggest single-year gain usually lands sophomore year, when the approach curve stops being an accident. Past 6'2", improvement comes two inches at a time and takes whole seasons. The other vertical event moves on a different schedule, shown in average pole vault height for high school. The girls' version of this climb, and why a two-inch bar step costs them more, is in average high jump for high school girls.

