This document discusses the differences between Basic Interpersonal Communicative Skills (BICS) and Cognitive Academic Language Proficiency (CALP). BICS refers to conversational language skills used in daily interaction, while CALP refers to the academic language needed for school. It takes 1-3 years to develop age-appropriate BICS but 5-7 years or longer to develop CALP. The Common Underlying Proficiency theory proposes that both languages share a common foundation of thinking and language processing skills. The document also defines bilingual education as a program where two languages are used equally for instruction.