As with many of the Mark Twain award nominated books, The War That Saved My Life is appropriate for most middle school grade students to read alone. Some fourth grade students will enjoy reading this alone but I think most would benefit from reading it with an adult. The facts that are presented relating to WWII might need to be explained as you read but would allow for a wonderful introduction into that time in our history. Ada faces cruelty due to a birth defect that was not corrected. While students might often read about cruelty it is usually not at the hands of a parent. So, this too might need to have a loving adult explanation with it.
Having said all this, I would recommend this book to families to read together. As with all great stories, by the end of the book I felt like I knew the characters. I wanted to know more about Ada, Jamie, Susan and even 'Mam". I found myself encouraging Jamie, respecting Susan and rooting for Ada. The ending was very satisfying and I'm looking forward to the sequel, "The War I Finally Won".