Is private schooling for children worth losing out on the opportunity to eat out as a family of 4 at a good restaurant every week (that's 250 per meal, so $1000 a month)?
Is funding your daughter's wedding (2000-10,000), worth skipping a vacation?
I think being middle-class is all about making choices between giving up luxuries of the body (e.g. resturant food), for luxuries of opportunity (e.g. schooling). If you are rich, you can have both your yatcht and private school. You can go to the country club, and keep a maid at the same time.
Being poor on the other hand is about making choices between necessities like "should we have water or power this week? pick one" or "should our food be nutritious or should we clean our clothes? pick one".