Objective: To investigate the infection status of group A streptococcus (GAS) among scarlet fever cases within the same class in schools experiencing clustering outbreaks and to analyze the factors associated with GAS detection, so as to provide a reference for the prevention and control of scarlet fever. Methods: All the classes with scarlet fever cases in schools reporting the clustering outbreaks of scarlet fever in Tianjin in 2023 were selected, and a total of 528 pharyngeal swab samples were collected from other students in the class for GAS isolation and identification except for the 97 patients. Conditional Logistic regression was used to analyze the influencing factors of GAS detection. Results: The overall positive rate of GAS among students in 15 classes from 12 clustering outbreaks with scarlet fever was 21.02%. There was a positive correlation between the positive rate of GAS detection in the class and the number of scarlet fever cases in the class ( r =0.82, P <0.01). The results of conditional Logistic regression analysis showed that pharyngeal pain ( OR=2.53, 95%CI =1.61-3.99) and tonsillar enlargement ( OR=1.90, 95%CI =1.15-3.14) of the sampled students were more likely to detect GAS positivity ( P <0.05). Conclusions In the clustered outbreak of scarlet fever in schools, students with sore throat and swollen tonsils who are in the same class as the case are more likely to be detected with GAS. During a school scarlet fever cluster outbreak, students with sore throat and swollen tonsils should be closely monitored and managed similarly to confirmed cases. At the same time, identifying close contacts in the affected class should not be restricted to those seated directly around the case.