Your Rankings determine your power, respect, and popularity. The rankings are not however like cliques. You are assigned Rankings by the school. So yes, the highest ranking tends to have the highest respect and popularity but not necessarily. You can increase your rankings by showing social and academic improvement .
For example let's say your the child of somebody famous and your in the the D range. That means your at the bottom average. So you can be popular but you wouldn't be the most popular student and you wouldn't have as much power or respect. So when you post don't have a whole bunch of attention on you because you'd be average.
Keep in mind this isn't a caste system. You can interact with the high ranking students you can even be friends with them they just would have more power and respect than you. Your rankings also depict your privileges like everybody has a single room, there are no roommates but maybe you have a bigger room or a bigger closet or maybe you have a personal guard.
The A students are the best of the best. They get the most respect and protection. A students can have personal guards and they're rooms tend to be wherever they want whether that be in the highest floor with the best view or the lowest floor for safety. A students where the A crest on their bags or clothes to symbolize who they are. Being an A student is a privilege.
The B students are above average but below the best. They still have more power but less protection. The B students instead get more freedom.
C Students are average. They get average privileges but no particular powers or lea way.
The D Students don't get any specific privileges. They are just below average.
E students and F students are given no special privileges but have more guarding. E and F students have to prove themselves the most and therefore are watched the most.