Socioeconomic factors.
Truth be told, I grew up in Geist and went private k-12 and a lot of my friends went the same route (graduated high school 08). Today, I live on the Marion County side of Geist and more and more kids are going to HSE/Mt. Vernon for high school, especially Mt. Vernon, if they aren't already in private school. Mt. Vernon and HSE are both closer in distance to that area in Lawrence Township than Lawrence Central.