Because Lexile levels are only used to determine a student's reading level, they are not useful in determining the student's overall grade level. MetaMetrics, the company that created the Lexile system, offers a list of ranges in which students of a particular grade should be on the Lexile scale.
The bell-curve-like shape of the Lexile ranges indicates at which reading level the majority of students in any given grade should be. For example, the majority of sixth graders should fall between 665L and 1000L on the Lexile scale.
Scholastic offers a guided reading scale with books that fit on the Lexile scale for increasing reading comprehension.