"I have homework..."
Or, "I have a test..."
And there's no good way for me to counter that argument. School is important, and it's very likely that their parents and their teachers have made it clear to them that school is most important. I could tell them that their relationship with God and other Christians is vastly more important than school, but then I might be leading them to disobey their parents. And lets be honest, some students are just dying for somebody to open that door for them.
But I do really think it's an issue that we make school the number one priority for kids. Again, I'm not downplaying its importance, but there are surely more important things. And for any Christian parents, you would think it'd be clear that your child's relationship with their Savior and the Creator of the universe would be more important than algebra, even just slightly. But sure enough, the philosophy tends to be, "I'll join that study/go to that event/read my Bible if I finish my homework first."
Active faith gets treated like an extracurricular activity. It's good to go to, but only if you get your real work out of the way first.
But this doesn't just stop at students. I think this mindset affects a lot of us, including myself. We fill our days with work and other things, and kind of leave whatever scraps of time we have for God. We don't make spending time with Him the priority in our life. Whether it's going to church, participating in a community group, praying or reading our Bible - we make it a secondary priority.
If we really made God our primary priority, it would mean making our faith the real work and everything else the secondary priority. And that might mean missing a phone call at work to volunteer in a ministry. Or taking a couple hours off from studying to go to a community group.
Otherwise, how is God different from any other extracurricular activity?