When I learned to teach languages nearly 30 years ago, the field was moving strongly toward an English-only approach.
At the time, I accepted this as best practice. But as a learner, I found that this approach actually made it harder for me to learn Spanish and French — especially when it came to understanding grammar efficiently.
Since then, both my teaching experience and the research have become more nuanced. While meaningful exposure to English clearly matters, research increasingly suggests that strategic use of a learner’s first language can support understanding rather than interfere with it, particularly when grammatical concepts already exist in both languages.
I also think it’s worth acknowledging a practical reality: many teacher-training programs assume multilingual classrooms, where English-only instruction is often the only workable option. That context matters — but it doesn’t always reflect the reality of one-to-one or linguistically homogeneous classrooms.