Generative AI offers strong potential for developing customized second language learning materials and tools. However, generating texts for absolute beginners—requiring strict lexical and grammatical control—remains a challenge. Although controlled text generation (CTG) techniques exist, they often require technical expertise and infrastructure, limiting accessibility for educators. This study evaluates, in the context of Spanish, a prompt-based approach that leverages large language models (LLMs) without fine-tuning or specialized tools. Prompts enforce linguistic constraints defined in two attachments: a categorized Spanish vocabulary list, and a set of example sentences illustrating approved Spanish grammatical structures organized by communicative function. Three variables were manipulated: AI model (ChatGPT-4o vs. Claude 3.5 Sonnet), prompt type (standard vs. extended, with constraint-enhancing techniques), and attachment format (rich-heavyweight vs. lightweight JSON). A secondary variable, text type (city descriptions, personal introductions, and dialogues), was also examined. A total of 720 texts were generated, 30 per condition. Measures included proportions of non-compliant lexical and grammatical items, user-perceived latency, and errors in vocabulary, grammar, and coherence. Model choice was the primary driver of constraint adherence, with Claude 3.5 Sonnet outperforming ChatGPT-4o. Extended prompts improved adherence across models. Attachment format showed no systematic effect on adherence, but JSON significantly reduced latency and response-time variability. Text type also influenced adherence, and error rates remained low. Findings offer educators a scalable, low-barrier solution for generating tailored beginner-level Spanish materials and AI-powered tools using LLMs, along with insights into how different design choices affect performance. This approach, transferable to other languages, provides a practical alternative to resource-intensive CTG techniques, addressing a critical gap in AI-assisted language education.
Getino-Diez et al. (Mon,) studied this question.