I needed an antidote to what I considered mediocre writing for young people and chose this book. This is one of my favorite books from childhood and I was fortunate to find an edition that has this book,
From the Mixed-up Files of Mrs. Basil E. Frankweiler, and The View from Saturday, all three excellent books, in a single hardback book on sale for about $4 (can't remember exactly how much I paid but it was really inexpensive and I was thrilled to have a copy on hand!). This book is about Elizabeth, who meets Jennifer, a witch, and becomes Jennifer's apprentice, so it even qualifies for the Hogwarts challenge. I just love E.L. Konigsburg, she is a top-notch writer and one of my favorites. Highly, highly recommended.