Underachievers/Unmotivated/Getting Away With "It"

I am starting to think that underachievers are mainly just unmotivated. What will keep students motivated? I think that a very attentive teacher is one thing and working at thier level helps to keep kids on track. However, we have so many things to do that if you let up for one minute, someone looses their motivation. All day long, I pull those kids back on track. They're right there and the poof! Gone! Lack of sleep seems to be affecting their motivation also. After weekends, motivation is low. They seem to stay on some sort of schedule during the week, then, Monday, it's all over again. The littlest thing can steer them off course. Writing on a tiny piece of paper, putting their head down on their desk, using the exuse of needing a drink of water to disrupt others motivation on the trip to the drinking fountain! I'm starting to discover that it's never ending...