As a stand alone story, this book is just OK. As far as prepping children for kindergarten book, despite the title, it is not very good.
The book is a collection of poems about kindergarten. The idea is that it takes you all the way through the first year of school, up to kindergarten graduation. It covers themes familiar to kindergarteners: getting ready for school, being nervous, having a nice teacher, losing teeth, field trips, growing out of clothes... things like that.
However, as far as getting ready for kindergarten, since so much of the focus is on what happens once a child is comfortable in the setting (like the 100th day of school and saying goodbye when moving on to grade one), it wouldn't be a book I'd recommend for this purpose. It does little to help children get ready for the transition.
I find the rhyme and rhythm to be clumsy, and other than one student who is Black (who's only participation in the book is shown being mean to the main character), there is little diversity.