How Syntactic Complexity Develops Across Grade Levels in Online Graded Reading Materials? Evidence From Clausal and Phrasal Indices

Syntactic complexity has long been recognized as a key indicator of text difficulty in graded reading materials. However, little is known about how specific syntactic structures are distributed across consecutive grade levels. The present study investigated fine‐grained clausal and phrasal complexity in online graded reading materials sampled from Newsela across nine grade levels using 22 syntactic indices. Results showed that syntactic complexity increased progressively with grade level but followed three broad bands (i.e., lower, middle, and upper grades), each with a distinct syntactic profile. Individual measures exhibited divergent patterns, but phrasal complexity was the dominant driver of grade‐level variation, yielding more significant indices, larger effect sizes, and a more sustained developmental trajectory than clausal complexity. Discriminant function analysis identified phrasal elaboration as the strongest discriminator of grade levels, with clausal coordination playing a secondary but substantial role. Based on these findings, we propose grade‐band syntactic benchmarks to guide language teachers in evaluating the syntactic complexity of graded reading materials within this genre.