Yes they will... i mean they will irrespective of ranks drag you down by 10-15 marks worst case if they perform badly. Essentially in terms of marks, you want all your classmates, and you to be close. What tends to happen is the lazy shits, will be brought up, while you will be brought down. (Don't use dumb, because some try but still don't achieve...there is absolutely nothing wrong with that at all). So where there would be a raw mark difference of 30 marks, it will end up about 10 which when you consider you study everyday (school day 4 hours, weekends up to 8 hours...they do zilch go to partys, chill with mates, the mark doesn't justify your hard work). It kind of makes my blood boil just thinking about it (wierd i know)
But aren't private schools meant to be quite good anyway?