In this link you'll find a table that gives approximate levels for each graded reader series by most of the major publishers. The scale goes from the Alphabet level (50 headwords) to Near Native (18,000 headwords), To see the scale, click here.
You can download or read ebooks for free in these sites:
READING ON THE GO: E-books in American English for tablets, e-readers, and mobile phones. The list includes some classic graded readers: http://www.americanenglish.state.gov/ebooks
How can students know their fluent reading level?
Pick up a book and read a little of it for a few minutes. As you read, ask yourself these questions:
- Can I read it without a dictionary?
- Am I reading it quickly?
- Do I understand almost everything?
If the answer is yes to each of these questions, then that book is appropriate to your level or you could try a higher level. If the answer is no to one of the questions, then you should go down levels until you have 3 yes answers.