For MMGM, I am recommending Flying Lessons & Other Stories by various authors, and edited by Ellen Oh.
Flying Lessons & Other Stories is not a typical middle grade book. It is a collection of short stories from various middle-grade authors, some new and some well-known, with an emphasis on diversity. This is not shocking, considering that the book is affiliated with We Need Diverse Books (a cofounder of which, Ellen Oh, edited the book). I love this book! Each story is interesting, usually being about 20 pages, the perfect length for their plots. It is very satisfying to read short stories by some of my favorite authors, such as Grace Lin (whose books I have recommended here and here). Several of the authors are even Newbery winners! I also love the diversity of the stories, especially since it is actually a major part of each story, as opposed to simply being a meaningless statement that does not change the story. This book is perfect for anyone, whether in school or just as a personal read, and makes a powerful statement about the importance of diversity in books.