Teachers use reading levels to mark a student's progress toward independent reading in the primary grades. This strategy lets each student move forward in reading at his own pace, while being measured by the teacher in comparison with other students and with a specific goal in mind. Primary books start at level A. These are picture books that are short and heavily illustrated, with fewer than six words on a page.
Primary reading levels A through F still include picture books, but by level F, students are reading more complex sentences with more punctuation, more new words and more complex ideas. At level F, the text is still repetitive and simple.
Primary reading levels G through L gradually introduce longer sentences, words with more syllables, and more complex ideas. Level L books are the earliest "chapter books," meaning they are longer and more detailed, while still offering copious illustrations.
The later primary grades are the time when students begin to read for information and to learn new concepts. At primary reading levels M through R, chapter books gradually become more complicated and can no longer be read in one sitting.
Reading levels S through Z offer the most challenging topics, sentence structure and depth of information for primary readers. At this point a young reader can be considered proficient and ready to move into ungraded books. Teachers continue to keep track of students' reading levels through a Lexile measurement system that grades reading ability in secondary grade levels. This lets the teacher continue to suggest or assign reading material that is at the right level of difficulty for each student.