You might try the TAKS online test center. It is the Texas site for all their standardized tests that have been released. The online tests are graded and show you what level the student is in relationship to other students. They also have printable tests that encompass the entire spectrum of testing. They are all free.

You won’t really find reading comprehension worksheets, like glurpy said, but there are several literature study guides out there for free that will help you in presenting book studies.

High schools don’t typically use reading comprehension worksheets (or at least, not where I live) which is why you are having a hard time finding them. They have the students read short stories, novels, poems, articles, etc., and then provide questions on what was read. You could try specifically searching for

short story questions
short story comprehension questions
novel study questions

and so on to narrow a bit more what you are looking for.

I looked everywhere but you have to buy them. But a good one is edhelper.com