Background - While the incidence rate of tuberculosis is low and declining at the national level, the department of Seine-Saint-Denis (SSD) has a higher incidence rate of tuberculosis (26.4 per 100,000 inhabitants in 2019 and 24.6 per 100,000 in 2015, the reference year for this case study) than the rest of metropolitan France (7.6 per 100,000 in 2019 and 7.0 per 100,000 in 2015), and than the Île-de-France region as a whole (16.4 per 100,000 in 2019, 14.5 per 100,000 in 2015). Method - In 2016, a micro-outbreak occurred in a primary school in SSD centered on an 11-year-old index case. Pediatric tuberculosis remains rare in France, and micro-outbreaks centered on sick children are rarely described in the literature. Using data collected by the SSD Tuberculosis Control Center (CLAT), we studied the factors associated with the risk of transmission and the considerations needed to adjust the scope of screening. Results - Within the school, 374 people were screened, 68 latent tuberculosis infections (LTIs) were identified, and 7 secondary tuberculosis cases were found. Most tuberculosis cases were concentrated on the same floor as the index case (6/7), and 3 secondary cases in the school were carriers of a strain identical to that of the index case. Conclusions - Even in the context of an index case under the age of 15, spatial proximity, duration of contact, and immune risk factors play a decisive role in the transmission of Mycobacterium tuberculosis and must be taken into account when selecting contacts for screening.