Seems like a crummy way to reach potential students, wouldn't you want to tap the local church's congregations? That is how the Catholic schools run in Seattle, though they don't have the same 20% non-Catholic full ride scholarship that they do in Portland (which made for a much better educational experience IMO).

The Summer Lunch Program (which has a much broader target audience/geographic area) in Seattle has experimented with online advertising, but had poor results. The keys to the kingdom really are reaching kids (and their parents) where they are, in schools, after school programs, and perhaps some online platforms (though the targeting is generally ineffective on Facebook/Google for this type of advertising).