In our school we use the Fountas and Pinnell Leveling System (also referred to as the Guided Reading Levels). In this system, students will be given a letter as their level. Second graders are typically be reading between the level H and M. Of course, since all student progress at their own rate, there will be students above and below this range. When your child works with me in a guided reading group and when they do independent reading time during reading, they are reading books on their level. In school we call this their "just right" level.
Since reading is so important, each student is expected to read at least 20 minutes each night. It is so important for your child to be reading "just right" books. This will help them become better and more fluent readers. There are a few ways to ensure your child is reading books on their level.
This website will give you a list of books on each level
When ordering books for the Scholastic Book Order, you can look for the GRL level below the books in the catalog.