Assignment Submission Rates

It's that time of year again - report writing season. And as I sit here endlessly crafting the most parent-friendly report comments I can, I have been struck by a common thread across far too many of my students' results.... They don't submit assignments. I mean, I did know that already - it didn't take sitting down to write reports to realise - but I don't understand WHY? I was such a conscientious student that the thought of not submitting something never even occurred to me! But my students just don't care about assignments. Most of them would only submit an assignment if it was an in-class one. Inevitably homework or take-home assignments, if submitted, are late and not to the same standard as they would be if done at school - and that's if they're submitted at all. For one assignment in one class, I had less than a 30% submission rate. Which is making me think - is it me? Is there something I can do to improve this submission rate? Aside from doing all our assignments in class, which takes up so much valuable time, how else can I support my students to get their work done?? I've just started using Edmodo and I can see the potential for it to help keep students on track outside of the classroom... But I haven't quite wrapped my head around how to do that effectively. As well as that, many of my students are from low socio-economic backgrounds and I really can't rely on them having reliable internet access from home. We have a lunchtime homework club, which attracts appallingly low numbers - and the kids who come would submit their assignments anyway, so it's not really helping the ones who don't submit. I know other teachers who keep students in at lunch until their assignment is submitted - but that's a huge time commitment and a very negative-reinforcement way to approach the issue in my mind. I want to foster an understanding of the importance of assignments, and an intrinsic motivation to achieve, in my students rather than have them submit assignments simply to avoid some form of punishment. So what to dooooo?