<p>In this meta-analysis, we aimed to examine teachers’ knowledge of language and literacy concepts and identify factors associated with variation in their knowledge. A comprehensive search of electronic databases, supplemented by hand searches and author contact, identified studies published between January 1994 and March 2025. Studies were eligible if they reported empirical data on PK–12 teachers’ knowledge of language or literacy concepts and provided sufficient information to compute standardized mean scores. A total of 143 studies met inclusion criteria, yielding 258 independent samples (a total of 22,727 participants). Outcomes included teachers’ knowledge of specific literacy concepts (e.g., phonological awareness, phonics, morphology), with moderators including teacher category, type of language and literacy concept measured, years of teaching experience, type of publication, and location. Random-effects meta-analysis and meta-regression revealed substantial heterogeneity across studies. Teacher category, type of language and literacy concept measured, and type of publication significantly moderated the standardized mean scores. Teachers of English as a foreign language demonstrated lower knowledge than other teacher groups, and teachers’ knowledge of morphology was significantly lower than knowledge of other literacy concepts, whereas knowledge of spelling exceeded that of reading fluency. Years of teaching experience and location were not significant moderators. Interpretation of these findings is limited by measurement variability, uneven sample distributions, and studies of lower methodological quality (shown in supplementary sensitivity analyses). These findings highlight systematic gaps in teachers’ literacy-related knowledge and underscore the need for targeted teacher education and professional development.</p>