This study reports year 1 findings from a multi-site cluster randomized controlled trial of a cognitive strategies approach to teaching text-based analytical writing for mainstreamed Latino English Language learners (ELLs) in 9 middle schools and 6 high schools. 103 English teachers were stratified by school and grade and then randomly assigned to the Pathway Project professional development intervention or control group. The Pathway Project trains teachers to use a pretest on-demand writing assessment to improve text-based analytical writing instruction for mainstreamed Latino ELLs who are able to participate in regular English classes. The intervention draws on well documented instructional frameworks for teaching mainstreamed ELLs. Such frameworks emphasize the merits of a cognitive strategies approach that supports these learners' English language development. Pathway teachers participated in 46 hours of training and learned how to apply cognitive strategies by using an on-demand writing assessment to help students understand, interpret, and write analytical essays about literature. Multilevel models revealed significant effects on an on-demand writing assessment (d = .35) and the California Standards Test in English Language Arts (d = .07).