An experimental approach to language training in second language acquisition: Focus on negation.

Researchers taught Spanish negation to 12 bilingual preschoolers. Half the kids already spoke good Spanish. The other half spoke mostly English.

Each child got two kinds of lessons. Some days the teacher spoke only Spanish. Other days she mixed Spanish and English in the same lesson. Kids earned stickers for correct answers.

Strong Spanish speakers learned negation no matter which lesson they got. Their English stayed steady.

Weak Spanish speakers lost English words when lessons were Spanish-only. When lessons used both languages, their English stayed safe and they still learned Spanish negation.

Zhou et al. (2026) later showed the same bilingual trick works for Chinese kids and even children with autism. They switched from short drills to quick intraverbal questions, but the idea stayed the same.

Michel et al. (2024) looked bilingual preschoolers with language disorder and saw vocab scores drop. That seems opposite, yet their kids had DLD while D et al.'s kids were typical. Weak systems need extra support; the methods clash because the learners differ.

Naresh et al. (2020) also protected first-language skills by keeping rich English mand opportunities all day. They echo D et al.'s warning: starve the first language and progress can slide.

If you run discrete trials with bilingual preschoolers, check the child's stronger language. When the home language is fragile, mix both languages in the same set of trials. A simple "No, this is not a perro, this is not a dog" keeps English alive while Spanish grows. One small change prevents backsliding and saves you months of re-teaching later.