M.R.
I think a lot of people whose children do not go to CPS or to neighborhood private schools do not understand the concept of the 8th grade graduation. Unlike a typical suburban school district, kids in the city (be it public or private) do not all advance to the same high school. For example, in my Chicago neighborhood the overwhelming majority of kids go to catholic schools and have several options for high school (Rice, Marist, McAuley, St. Ignatius, Mt. Carmel, Queen of Peace, Chicago AG, St. Rita's, St. Laurance, Morgan Park Academy, and this is even before one would consider the highly selective magnet high schools or academies!). This is their last hurrah as a group of friends and the graduation from 8th grade is actually a big deal.
So...I completely get where you are coming from! This is a huge deal for the kids. Given that it will be June and you have a large number of people possibly attending, I would think that a backyard or forest preserve barbeque would be appropriate and make it open house style.