I was having lunch with a Church College Minister friend when he said the words I've heard lots and lots of times, "Why do local college students drop out?". His church is known for being serious about College Ministry and for having a strong one.
My home church is one that has asked that question lots of times. In my experience in this one place, I have seen those churches that do well keeping their own students involved don't seem to do well in reaching out of town students. And, the churches who do well reaching out of town students have struggled and often failed in keeping their own connected.
During the Spring Semester a year ago when I served as the Interim College Minister at my home church, I made a concerted effort to re-connect local students who had grown up in our church. I experienced 99% failure in that area. The previous College Minister had spent his first summer having all the local graduates in his home weekly for a Bible Study and had averaged about 30 per week. Wow! He had made a turn around. When school started in the fall and the ministry went back to their regular fall events, one...ONE of those 30 came once...ONCE!
As you already know, I don't have a magic answer, but here is what I think. They feel like strangers in their own church and it offends them! A local told me he went to the first big fall event at his home church College Ministry his Freshman year and got mad. When he walked in the door, a student he had never seen held out his hand and said, "Welcome to________Baptist Church". It was an out of town upperclassmen doing what we teach them to do. He was welcoming someone he did not know.
Yet, you say what about all those that didn't even come once? I still believe there is some fear there about all the strangers in "my home church".
Here is one thing I would try. I would enlist as many locals as possible to serve as Greeters, Welcome Table Personnel, etc for those first few weeks. I would pair them with an out of town upperclassmam and introduce them in advance. They would have a reason to be there. They would already know an upperclassman. And, they would recognize and welcome other locals. This would help prevent others being treated as strangers in their home church.
I have always worked at having a balance of guys and girls up on stage in "face roles". I would also work at having a balance of locals and out of towners in "face roles". if you have some sort of leadership team, I would ask some locals to serve on it.
No one likes to feel like a stranger......especially not at home!