In the United States students attend school 180 days per year. From kindergarten to 12th grade is 13 years. 180 days per year times 13 years in school = 2,340 days in school, about 19,000 hours or so (if they are in school 8 hours, some schools are more and some are less).
The total number of days in school is 2,340 between 0-18 years old.
In that same time period, you have 6,570 days in total, so about 35% of that would be spent in school.