My students kept losing their index card with their username and password on it. I made these "bookmarks" so that they could easily find them, and the larger font helps them log in easily. You can write or type their username and password on the bookmark. I print them out on cardstock and highlight their book level so that they always have their range handy when picking out books. You can also laminate the bookmark and use a color wet-erase marker to highlight their book level. I've also put these on a ring so that if a student loses their bookmark, they can find it on the ring.
You can edit the bookmark with your own AR book levels. These are the levels that I use for my first grade class. Just type over the sample usernames and passwords!