My archdiocese has I think the third-largest parochial school district in the U.S. in terms of enrollment, but things haven't been really good for them in a while. The local deaneries have been working on plans for school closures for several years now, just because of shrinking family size and the tendency of families with children to want to move to suburbia for a larger house; the city parishes are dealing with aging parishioners and declining enrollment. Our grade school is safe from this -- I think we have 9 new families this year coming in from neighboring parishes whose schools may be closing soon. However, ours is the second most-affluent parish in the metro area, and the principal reports that number of families on the extended-payment financing plan is WAY up this year. (Using the plan costs $200 in interest/fees. Previously most of our families paid in advance to avoid that.)
The suburban parishes and the Diocesan high schools are seeing enrollment effects from the economy, and that is a lot more telling than our experiences in the city. A story this morning in our local newspaper was talking about cost-cutting in high school sports programs, and they mentioned that enrollment at the most affluent diocesan high school in this area was down to 375 students this year, from 500 last year.
The prep high schools and the independent schools are probably fine, because they are very competitive and have long waiting lists.
PS: Parochial grade school here (Catholic or Lutheran) costs an avg. of $5K. Diocesan HS is around $8K, and the preps start at around $10K and go up to slightly over $14K. The Catholic schools have a HUGE multiple-child discount, though -- at ours 3 children will only cost $700 more than one child, and there is no add'l fee starting with the fourth child on up.) The independent schools tend to charge in the low $20K range for HS. We also have some affluent school districts that take paying pupils; that tends to run around $11K (they do it because their enrollment is down -- in this economy REALLY expensive homes tend to be a splurge for the childless who have more disposable income.)