An extensive body of research has investigated the role of syntactic complexity in gauging the linguistic complexity of reading texts, particularly for the purpose of determining their grade appropriateness. However, little such research has focused on adapted teaching materials for English as a foreign language (EFL) contexts, and to date there has been no systematic effort in establishing syntactic complexity benchmarks to guide text adaptation practices in such contexts. This paper reports on a large-scale study that assessed the quantitative differences in syntactic complexity among adapted teaching materials for different grade levels in the EFL curricula in China. Our data consisted of 3,368 adapted English texts solicited from a corpus of teaching materials approved for use in the 12 primary and secondary grade levels in China by the Chinese Ministry of Education. All texts were analyzed using 8 syntactic complexity measures representing different dimensions of syntactic complexity. All 8 measures showed significant between-level differences with moderate to large effect sizes and nonuniform patterns of progression, and 5 measures were identified as significant predictors of grade levels in a logistic regression analysis. The implications of our results for establishing syntactic complexity benchmarks to inform future text adaptation practices are discussed.