The document discusses using proficiency testing to improve instruction for English learners. It summarizes the WIDA consortium, which advances academic language development for PreK-12 English learners through standards, assessment, research, and professional development. It also discusses CELLA testing, which assesses English proficiency in listening, speaking, reading and writing, and Krashen's theory of second language acquisition, which includes the acquisition-learning distinction and hypotheses about natural order, input, monitoring, and affective filters.