In Schiffer's final sentence is the key: "Maybe next year, when a teacher tells them again, the Good News will fall on good soil and will stir their hearts to Faith."
The Good News, the kerygma, is the key to all of this. Young people need to hear over and over why the teachings of God/the Church matter. It's the same issue I once encountered when a 7th grade girl asked me, point blank: "Why should I do anything God wants?"
Someone who has no relationship with the God of love and mercy will not understand God's desires for our behavior. Of course they tune us out. The other messages from the culture about "me first" are much louder and more attractive than we are... but that's because we deliver our message without conviction, minus the fire of the Holy Spirit. We often teach doctrine (especially those "rules" about sexuality) as if it exists apart from the love of God. We need, as Pope John Paul II did in his Theology of the Body, to connect these things continually to the love of God and God's plan for good for each person and for the world.
Pope Francis pretty much nails it in section 165 of Evangelii Gaudium:
We must not think that in catechesis the kerygma gives way to a supposedly more “solid” formation. Nothing is more solid, profound, secure, meaningful and wisdom-filled than that initial proclamation. All Christian formation consists of entering more deeply into the kerygma, which is reflected in and constantly illumines, the work of catechesis, thereby enabling us to understand more fully the significance of every subject which the latter treats. It is the message capable of responding to the desire for the infinite which abides in every human heart. The centrality of the kerygma calls for stressing those elements which are most needed today: it has to express God’s saving love which precedes any moral and religious obligation on our part; it should not impose the truth but appeal to freedom; it should be marked by joy, encouragement, liveliness and a harmonious balance which will not reduce preaching to a few doctrines which are at times more philosophical than evangelical. All this demands on the part of the evangelizer certain attitudes which foster openness to the message: approachability, readiness for dialogue, patience, a warmth and welcome which is non-judgmental.That's the key. We don't evangelize young people a little every once in a while, at a retreat, by giving a witness talk, or providing the occasional meditative prayer or meaningful service experience. We must continually connect EVERYTHING we teach to the Good News. The Church teaches X because God loves you and wants you to have a fruitful life that builds up his Kingdom, not simply the Church teaches X: do it.
Never. Stop. Evangelizing.