For public schools, they simply take the total number of schools that field girls lacrosse teams and divide them into 4 categories evenly (4A, 3A, 2A, 1A) based solely on the schools enrollment. 25% of schools are 4A, 25% are 3A, 25% 2A and 25% 1A. This is done every 2-3 years and schools stay in their category for that time period..