Volunteers must be proficient in both Spanish and English to serve as tutors. Most Spanish speakers seeking English lessons through ESL on the Go have basic or minimal English skills. Thus, volunteers must be able to explain English grammar concepts in Spanish and answer technical questions about the English language. However, if Spanish speakers with intermediate to advanced English skills seek English lessons, volunteers with a lower Spanish proficiency may work with them, as these lessons require fewer explanations in Spanish and focus more on English conversation practice.