From what I’ve seen so far, MetaMetrics seems to allocate a fixed number between grades – 150 Lexiles – going up in equal increments between grades? That doesn’t seem very scientific.

Students’ Lexile scores, on average, increase 75L to 150L over the course of a year. However, the Lexile range of individual students within a specific grade/year can vary by as much as 300L or more.

All the research that MetaMetrics and Scholastic have done shows that students in younger grades/years demonstrate greater Lexile growth than ages 13-14 and above. That is because students are still acquiring vocabulary and reading skills at a faster rate as they are developing proficiency than their older peers.