Benson Hines has a great discussion about integration of college ministry relative to mission here.

This has been a consistent struggle for us in the College Ministry at The Austin Stone, but definitely one that has yielded great fruit in ministry.  To summarize where we have landed, we:

1. Deliberately integrate our weekly worship service, and will NOT begin a separate service just for college students.
2. Provide specific environments and a few events aimed at assimilating college students, including a worship service on campus once per semester (Austin Stone on Campus audio and review).
3. Deliberately integrate students into ministry opportunities that serve the church and serve our city.  Any opportunity that exists in open for any college student to participate, and we encourage students in that direction.
4. We contextualize our missional community structure to mobilize students onto campus, and therefore have a separate ministry that is under the leadership of our overall missional community structure, but operates relatively independently.
5. We have both integration and separation in our equipping ministry and global missions ministry.  There are specific opportunities just for students that equip and mobilize based on their schedule and life stage, but also students are welcome to engage in any of our other course/seminar/training environments and global mission opportunities.

There is never a perfect answer, but this has been an effective solution that affords opportunities for students to connect with people outside their lifestage, but also keep them invested in their mission field.