Times are different these days. Kids are growing up in a world of microwaves, fast food chains, Nintendo, Wifi, iPads, along with a ton of other technical marvels.
It is amazing the difference in effort you will get from worksheet to worksheet. Granted the amount of effort may vary immensely from year to year depending on the group of students you have.
As a middle-school math teacher, I have seen many students who do understand abstract concepts, and even enjoy learning about things like Pi and the Pythagorean Theorem, but who appear to be unable to do so due to a weak grasp of math fundamentals.
Or you can usually find textbooks and workbooks at the public library, where you can also copy any worksheets that you want to use.