When I cut out the Internet from their computers in order to get them to do something useful

That's called micro-managing. I don't believe it has any useful effect. The fact that you're ABLE to do so, doesn't mean you SHOULD. If kids don't turn-in their assignments, they get bad grades. It's true whether they're watching TV instead of doing their homework, or browsing the internet instead of doing their computer course work.

if kids are not interested in doing what they are supposed to do, they will always find something else to do.

Indeed. And the kind of controls teachers / administrators put on computers to try and force kids to do their extremely narrowly-defined coursework, is monumentally detrimental to kids actually learning how to use a computer. That only results in rote memorization and following rigidly defined step, and further becomes a tremendously onerous atmosphere where the most basic exploration is brutally punished...

Frankly, NOTHING you can teach them in that locked-down atmosphere, is anything worth learning. I would rather see the money spent on computer labs go to other projects.