Ok kiddo, imagine you and all your classmates are like little books in a library. Some of you are big books with lots of pages, and some of you are smaller books with fewer pages.
Now, imagine your teacher reads all the books and decides which ones are the best. They might look at things like how many words are in the book, how hard the words are, and how interesting the story is.
When your teacher is done, they put all the books in order from best to worst. The book that's the best is at the top of the shelf, and the worst book is at the bottom.
So, class rank is kind of like that. It's a way of saying which student is the best in the class and which one is the worst. But instead of looking at things like the number of pages or how interesting you are, they look at things like your grades and how well you're doing in school.
The student with the best grades and who is doing really well in school is at the top of the class rank, and the student who is struggling and not doing as well is at the bottom.
It's important to remember though, kiddo, that class rank isn't everything. It's just one way of measuring how you're doing in school. And sometimes, even if you're not at the top of the class rank, you can still be really great and successful in other ways.