Take an 8.5 x 11 piece of paper. Circa punch one of the narrow edges. Fold it in half, leaving a little bit of margin so that the holes are clear. You can now put a letter-sized sheet into a junior-sized Levenger notebook.
I do a lot of my brainstorming on 11 x 17 sheets. Those don't fit *anywhere.* But fold them in half, and you get 8.5 x 11.
I also like to turn a junior-sized notebook sideways, creating a more portable 8.5 x 11 spread. Works better with blank or grid-ruled, rather than lined pages.
Thanks for the idea. I've never really used grid paper (as an adult ) but I bought some and I'm using it with my Levenger foldover JR. Size notebook. So far so good!!