On a recent Tuesday evening, seven students gathered at the Dance Palace for their weekly Spanish class. During the two-hour session, not a word of English was spoken by their teacher, Laura Alderdice. Instead, Ms. Alderdice guided the class entirely in Spanish, embracing the full-immersion approach that helped her become fluent decades ago. Following her lead, the beginner students searched for words and puzzled through verb tenses while describing what they did that day.