I'm finally realizing that I have to be supremely structured about book check-out time, otherwise chaos ensues. My chance to observe my colleague Juanita James (at Pillsbury) enabled me to see how she handles her time with no help whatsoever. Once she got her kids settled in the project for the day, she dismissed groups to go check out books and bopped back and forth from working students to the circulation desk. I tried this a bit with my 4th graders last year, and it was fairly effective, however the layout of my media center with the computer lab a good piece away from the bookshelves made it nearly impossible to flutter between two groups of kids. So, I've trained. And had to create projects that make it easy for students to work independently (or get help from classmates) while I check out books.
Sometimes that's more detailed than it seems necessary. For example, today I had to break up a group of first graders into thirds so that I could show them where books in their reading level were stored, and rely on my superb grouping skills (taking a third of the sassy kids with me in each group) so that the remaining workers were relatively well behaved. It actually felt less chaotic than usual, and enabled me to help kids find books they like on a more individual basis, which I haven't had time to do before.
Its definitely a work-in-progress, but I'm seeing progress.