How Kindergarten Teachers Adapt Their Speech for Children: Acoustic Evidence and Educational Implications from Mandarin Child-Directed Speech

Teachers play a central role in shaping children’s early language environments through the way they speak. Child-directed speech (CDS), characterized by distinct acoustic and prosodic adjustments, has been shown to facilitate children’s phonetic perception and language learning. This study investigates how Mandarin-speaking kindergarten teachers adapt their speech when addressing children compared to adults. Speech samples were collected from 35 female teachers using interactive puppet-based scenarios featuring Peppa Pig and Xiong Da. Acoustic analyses focused on the corner vowels /a/, /i/, and /u/, examining mean fundamental frequency (F0), F0 range, the first (F1) and second (F2) formant frequencies, and vowel space area (VSA). Results revealed that, relative to adult-directed speech (ADS), teachers’ CDS showed significantly longer vowel durations for /a/, /i/, and /u/ (all p < 0.001, surviving Bonferroni correction). In addition, descriptive trends—which did not survive Bonferroni correction—were observed for wider F0 range for /a/ (uncorrected p = 0.004), higher F2 for /a/ (uncorrected p = 0.011), and higher mean F0 for /u/ (uncorrected p = 0.002); these effects should be interpreted with caution and are not considered statistically significant in the present study. Vowel space area did not differ significantly between CDS and ADS. These findings indicate systematic adaptations in prosodic and temporal features—particularly duration and pitch variability—though not all acoustic measures showed significant changes. Beyond acoustic distinctions, the results underscore teachers’ active role in modulating their speech to support early language development. The study contributes to understanding how Mandarin-speaking kindergarten teachers acoustically adapt their speech to children and offers preliminary insights that may inform future research on teacher speech-training and early-childhood communication practices.