Moisture damage can influence the subjective assessment of indoor air quality (subjective IAQ) in various ways. We studied whether the frequency of symptoms reported across students at school level mediates the relationship between observed mold and dampness in a school building and students’ subjective IAQ. To answer this research question, we tested a multilevel path model.

The analyzed data was created by merging two nationwide data sets: 1) survey data from students, including information on subjective IAQ (N = 24,786 students); 2) data from schools, including information on mold and dampness in a school building (N = 222).

After the background variables were adjusted, schools’ observed mold and dampness was directly and significantly related to poor subjective IAQ (standardized beta (β)= 0.22, p = 0.002). In addition, in schools with mold and dampness, students reported significantly more symptoms (β = 0.22, p = 0.023) than in schools without; the higher the prevalence of symptoms at school level, the worse the students’ subjective IAQ (β = 0.60, p < 0.001). This indirect path was significant (p = 0.023). In total, schools’ observed mold and dampness and student‐reported symptoms explained 52 % of the between‐school variance in subjective IAQ.