An acclaimed author and a #1 New York Times bestselling illustrator team up to bring us a funny, warm, and utterly winning chapter book that follows, day by day, the first hundred days in one first grader's classroom.

In just one hundred days, Harry will learn how to overcome first-day jitters, what a "family circle" is, why guinea pigs aren't scary after all, what a silent "e" is about, how to count to 100 in tons of different ways, and much more. He'll make great friends, celebrate lots of holidays, and learn how to use his words. In other words, he will become an expert first grader.

Made up of one hundred short chapters and accompanied by tons of energetic illustrations from bestselling illustrator of The Good Egg and The Bad Seed, this is a chapter book all first graders will relate to - one that captures all the joys and sorrows of the first hundred days of school.