It's like most types of schools to an extent, just a larger range of mixed ability pupils.
Facilities aren't always great and class sizes are bigger.
There's probably a bit more disruption, but that does depend on the area your school is in etc.
You also sound like an absolute (insert any chosen insult). You're online for god's sake, speak with some informality - you go to a grammar school (if you're using the correct meaning), you're not paying £15000 a year to go to a private school.