This is something I used to worry about with the kids... if one kid does really well in school, then the teacher's expectations can be so high for the next child!
At some point though, I just stopped worrying about it... I have no idea which kid will do well in school! One will surge ahead and then the other will seem to plateau... then a month later, it reverses. I figure there's no point in worrying about something we have no control over!
I know a lot of people who really wrestled with this though, so it's still there in the back of my mind as something to think about when the kids get older.
Did you have an older sibling you felt you had to live up to (or vice versa: have a younger sibling who felt they had to live up to you)? How did it impact your relationship with your siblings?