A Systematic Mapping of Grey Literature on K–12 School Acoustic Design

Classroom acoustic conditions significantly affect students’ learning outcomes and teachers’ occupational health, yet a systematic gap persists between optimal acoustic standards established in research and their implementation in practice. Although peer-reviewed literature has defined performance thresholds, guidance on which design strategies effectively achieve these targets across different school spaces remains limited. Grey literature—project documentation from architectural firms, acoustic consultants, and material suppliers—contains valuable practice-based evidence. This study aimed to map practice-based evidence in K–12 school acoustic design, identify dominant space–strategy patterns, and appraise evidence quality through systematic mapping of grey literature. Following PRISMA-ScR guidelines, systematic searches were conducted across 27 websites representing three source types, yielding 142 projects from 22 countries. Data extraction employed a standardised coding framework encompassing project metadata, 19 space types, and 16 acoustic strategy subcategories within five major categories. Evidence quality was assessed using a quantified AACODS framework (score range 6–30), with inter-rater reliability (ICC = 0.989). The evidence landscape revealed geographic concentration in North America (41.5%) and the Asia–Pacific region (26.8%), with architectural firms contributing most documentation (54.2%). Space–strategy analysis identified dominant patterns: classrooms and corridors primarily employed absorptive ceilings combined with wall treatment, gymnasiums relied on suspended absorbers, and performance spaces used multi-strategy packages including variable acoustics systems. Open-plan learning spaces displayed high strategy diversity without consensus solutions. Mean quality score was 15.2/30 (SD = 3.0), with only 16.9% of projects reporting quantitative performance indicators. These findings reveal a substantial research-to-practice gap and provide an empirical basis for developing targeted acoustic design guidance for practitioners, informing policy, standards, and future research directions.