unproductive
Not giving useful results, even when effort is used.
Unproductive means failing to produce useful results or accomplish anything worthwhile. When you spend an hour doing homework but end up daydreaming, doodling, and checking the clock instead of actually finishing your assignment, that's an unproductive hour. The time passed, but nothing got done.
A meeting becomes unproductive when people talk in circles without making decisions or solving problems. An unproductive day at school might mean you were physically present but your mind wandered, and you didn't learn much. A garden plot is unproductive if nothing grows there, no matter how much effort you put in.
Notice that unproductive doesn't always mean lazy. You can work very hard and still be unproductive if your effort doesn't lead anywhere useful. Raking leaves during a windstorm might take lots of energy, but it's unproductive because the wind just blows more leaves back onto your yard.