The way it's typically done in the US is via standardized test scores. If you search a particular school, most likely you'll end up at greatschools.org, a website that ranks schools solely on the most recent standardized test scores available.
Obviously this ranking system leaves much to be desired, particularly for those who realize the flawed nature of standardization and high stakes testing. There is no attention paid to any of the important features of a school that research has proven to be crucial for student learning. These include class size, recess time, parent/community involvement, teacher collaboration/support, and student interest level, just to name a few.
It pains me that some parents select their child's school based solely on a group of test scores that have little application to the world. Standardized tests, after all, cannot measure some of the more important life skills such as problem solving, creativity, social skills, and compassion.
So why then, are we basing such an important decision--where to send our children to school-- on these functionally useless test scores?
