Background <p>Scarlet fever, caused by group A <i>streptococcus</i> (GAS), has resurged globally since the early 2010s. Although schools and pre-schools are well acknowledged as the high-risk settings for scarlet fever outbreaks, little is known about the effect of school terms on scarlet fever epidemics among pre-school-aged and school-aged children. In this study, we aimed to understand the role of school terms in scarlet fever epidemics by leveraging a population-based surveillance across 15 years in China.</p> Methods <p>We included weekly scarlet fever cases from 2005 to 2019 in Liaoning Province (one of the provinces with highest incidence of scarlet fever) among children aged ≤ 12 years who were subsequently categorised into three groups: school-attending, pre-school-attending, and non-pre-school-attending. We used wavelet spectrum analysis to identify periodicity patterns of scarlet fever epidemics. We applied negative binomial regression models to estimate the relative risk (RR) of scarlet fever associated with school terms and population categories, adjusting for background risk of infection, meteorological factors, and temporal trends.</p> Results <p>A total of 64,950 scarlet fever cases were identified, with non-pre-school-attending children, pre-school-attending children and school-attending children accounting for 16%, 44%, and 40%, respectively. Scarlet fever exhibited a significant semi-annual pattern, usually peaking in May to June (during the spring semester) and November to December (during the autumn semester), with substantial declines during school breaks. Wavelet analysis identified this strong semi-annual signal, plus an additional 3.3-year (171-week) periodicity signal. Compared to non-pre-school-attending children during school breaks, school term was associated with a 2-fold higher risk of scarlet fever in pre-school-attending children (relative risk [RR] 2.14, 95% confidence interval [CI] 1.94–2.36) and school-attending children (RR 2.07, 95% CI 1.88–2.27), whereas a reduced risk was observed in non-pre-school-attending children (RR 0.84, 95% CI 0.77–0.91). During school breaks, pre-school-attending children remained at higher risk than non-pre-school-attending children (RR 1.80, 95% CI 1.63–1.99), while school-attending children showed no significantly increased risk (RR 0.97, 95% CI 0.88–1.08). Further stratification by school semester indicated that the association between school term and scarlet fever risk for pre-school-attending children and school-attending children was stronger in the autumn semester than in the spring semester.</p> Conclusions <p>School terms have differential effects on scarlet fever risk across population categories. School-attending children have a higher risk for scarlet fever during school terms while pre-school-attending children have a higher risk for scarlet fever all year round than non-pre-school-attending children. By contrast, the risk decreases among non-pre-school-attending children during school terms. These findings support the development of targeted public health interventions to mitigate scarlet fever outbreaks in high-incidence regions.</p>