Inside/Out– Prep, train, and educate kids and sent them out into the world to do evangelism. Basically you go a non-believer on their turf.
Outside/In– Throw events and get non-believers into your youth room. Basically you take a non-believer put him/her on your turf.
Obviously, in order to be missional it is imperative to send our kids out into the world. Many non-believing students have a very negative perspective about church and Christians, which sucks but it is the reality we have to work with. So youth ministries have to work very hard to project a positive, non-arrogant, and nonjudgmental feel towards non-believers when we go onto their turf. Going to them is huge because they already feel comfortable, secure, and safe, which is essential when striking up a conversation about God. Once we expose them to church land there is an instant intimidation and weirdness factor that is attached to being in a church setting. If we really think about it… our youth ministries are weird. We singing unfamiliar songs, we have a christian code language, we use this foreign book, we accept everyone, and we know how to have some good sober fun. If we meet non-Christians on their turf and build a strong relationship with them, we can start talking about God and hopefully and prayerfully invite them to church. We should give them a taste of Jesus and if they want more they should know where to find it.
My point: Youth ministries need to focus on the sending OUT aspect of evangelism.
Pete Ward has an excellent book titled: God At The Mall, that I highly recommend.