The Oral Language Development Series is a set of research-based language readers designed with an eye to helping English language learners (ELLs) improve their oral language skills. It comes with a detailed teacher’s guide explaining how the series works. The leveling is organized around language structures, from simple sentences up through more complicated multi-clause sentences. The books can also be used for other literacy purposes, such as guided reading. There are 102 books in the set. For additional information about OLDS including videos, articles and other related content, view our complete list of oral language resources.