Late talkers, despite achieving normal language test scores by age five, often face enduring conversational challenges. This study examines whether school-age children identified as late talkers at 24 months show persistent disruptions in speech and lexical entrainment. We analysed spontaneous conversational samples from 36 late talkers and 37 typically developing five-year-olds, examining lexical entrainment patterns in high-frequency, hedge, and affirmative cue words and speech entrainment of 412 acoustic features (rhythmic, articulatory, and phonatory dimensions). Perceptual conversational quality scores were provided by raters, while cross-recurrence quantification analysis measured speech entrainment patterns. Sham conversations and machine learning identified key predictors distinguishing late talkers from controls. Our results revealed that late talkers perceptually exhibited lower conversational quality. Late talkers showed significantly lower lexical entrainment in high-frequency words but comparable use of hedge words and increased use of affirmative cue words. In speech entrainment, late talkers exhibited intermittent rather than consistent entrainment. They also exhibited more frequent but less complex speech entrainment, showing repetitive interaction patterns. Notably, late-talking children exhibited marked rigidity in articulation and reduced complexity, intermittent rhythmic entrainment, and weaker phonatory control. Finally, seven unique feature-measure matrices in late talkers, reflecting articulation and phonation stability and complexity, were significantly associated with poor conversational quality in this group. Within the framework of the Interactive Alignment Model, these findings underscore persistent disruptions in automatic entrainment processes among late talkers, contributing to reduced conversational quality.