Which one is correct?
- I go to school by foot.
- I go to school on foot.
"By" in this context normally refers to a mode of transportation whereas "in" or "on" would refer to your position whilst travelling.
This suggests we are using a car to travel.
This implies we are inside of a car while traveling.
When it comes to using "on foot" or "by foot," either would be correct; however, a quick google search demonstrated that "by foot" is more commonly used (150M hits vs. 85.4M hits)