The Clue Adjust, as edges when putting on school-book cover
The Answer ALIGN
The word "align" means to arrange things in a straight line or to adjust them so they are even. When putting a cover on a school book, you often need to make sure the edges match up perfectly. This process is about adjusting the cover so it fits nicely, which is exactly what "align" describes. Therefore, "align" is a fitting answer to the crossword clue.