Large-scale early childhood studies use the first two subscales of the Preschool Language Assessment Scale, "Simon Says" and "Art Show" (PreLAS2000; Duncan & De Avila, 1998) to guide decisions about the most appropriate language (or languages) researchers should use when directly assessing the academic skills of dual language learner (DLL) children. Large-scale studies use a cut-score derived from a total score on the two PreLAS subscales in English and/or Spanish in combination with parent or teacher reports of children's language abilities, to route children into the most appropriate language of assessment. However, limited research exists to support the use of these cut-scores as part of a language routing procedure with Spanish-speaking DLL preschool children from low-income backgrounds. The current study examined the validity of the two English PreLAS subscale scores for a local sample of children enrolled in Head Start (N = 872) and Hispanic children from the national FACES 2006 sample (N = 935). Rasch and DIF analyses supported the invariance of item difficulty values across the three- and four-year-old age groups in the overall sample. For a subsample of Spanish-speaking DLL children, receiver operator characteristic (ROC) analyses identified the most appropriate cut-scores on the PreLAS screener for both age groups. Findings provided evidence to support the validity of the use of the English PreLAS language screener score as part of a more comprehensive language routing procedure. Implications for policy, practice, and measurement development are discussed. (author abstract)