After going over a fair amount of the book, i was wondering if you could coordinate pictures closer to the actual text that is talking about what is going on in an image. In some cases the image is 2 pages further down the line. For beginners, it is important to keep the images and text going with it in phase with each other (aka. on the same page). I am not sure what the budget extent of the book is, but if there is wiggle room it may be worth sacrificing some blank paper space to keep each text area on the same page as the diagram / illustration. In higher level books you can usually forgo this know that your readers will get the jist. But in a beginners level book it is important to keep supporting images with the text that is written with it as much as possible.
Sort of like how the Illustrated Pomodoro technique is being set up. Being a text book I know this makes this whole process more difficult. But perhaps an additional aid then… An outline of the Illustrations (in miniature monochrome) in the outside margins of the book (type set to the right on odd number pages, and to the left on even pages) but labeled with “Name”, “figure number”, and “the page that the fully illustrated diagram can be found on. Hopefully by the next page, to make flipping back and forth a minimal distraction. These mini illustrations would of course be Hyper-linked to the pages with the full size illustration, and of course hyperlinked backed, again to give us PDF only readers a minimal distraction factor while they work.