Liping Ma’s Knowing and Teaching Elementary Mathematics (note: this link takes you to the 2nd edition at the publisher’s website; you can still purchase the 1st edition from other sources including Amazon) is a fantastic book for anyone who teaches math—elementary or secondary.
Briefly, Ma contrasts how math is taught in China with how it’s typically taught in the U.S. by asking teachers from both countries how they teach four topics: subtraction with regrouping, multi-digit multiplication, division by fractions, and the relationship between area and perimeter. Read this book and, at a minimum, you’re going to teach these four topics differently—and more effectively!—than you ever have. (Light bulbs especially went on for me when I read the subtraction and fraction chapters!). And to the extent you can generalize to your practice the ways in which Chinese teachers’ approaches are more effective than those of U.S. teachers, you’re going to be a better math teacher overall.
So if you’re looking to enhance your math instruction for next year, put Knowing and Teaching Elementary Mathematics at the top of your summer reading list.