Early childhood education and care (ECEC) programs across the United States are experiencing an increasing level of linguistic and cultural diversity among the children they serve. Dual Language Learners (DLLs)--young children who grow up speaking more than one language at home and in the classroom--bring to these classrooms unique learning strengths, experiences, and challenges. And while considerable research has explored effective teaching practices for DLLs in bilingual classroom settings, far less is known about what works in superdiverse contexts, where the children in a class speak a wider variety of languages. This report examines teaching practices that can successfully support the learning and development of DLLs in linguistically diverse ECEC programs. It draws on interviews with educators and program directors; focus group discussions and surveys with families; classroom observations; and the collection of classroom artifacts from six preschool classrooms. The classrooms chosen were nominated by their local communities for providing exemplary and high-quality early learning opportunities for DLLs, and include three program types: Head Start, public pre-kindergarten (pre-K), and private preschools. Teacher and program language use across these different contexts was investigated to deepen understanding of effective practices and to identify examples of exemplary teaching. (author abstract)