Introduction.Tuberculosis continues to be a common problem in settings of socioeconomic vulnerability. Our primary objective was to establish the prevalence of latent infection and tuberculin conversion among school contacts of tuberculosis cases. Population and methods.In a programmatic area in the south of the City of Buenos Aires, the prevalence of latent infection and tuberculin conversion was assessed in 691 children and adolescents using the tuberculin skin test. The association between loss to follow-up by the health care team and the demographic, school, and baseline care characteristics was studied, and the level of adherence when isoniazid chemoprophylaxis was indicated was described.Results. According to established definitions, the prevalence of latent infection was between 3.4% (95% confidence interval [CI]: 2.3-5.2) and 11.6% (95% CI: 9.3-14.4) in the 610 contacts with at least one skin test. The incidence of tuberculin conversion was between 0.3% and 6.8% in the 294 assessed participants. Age older than 18 years, a higher prevalence of unmet basic needs in the school district, attending the afternoon school shift, negative sputum smear results in the index case, and absence of baseline skin test were associated with contact lost to follow-up.Conclusions. The incidence of tuberculin conversion among school contacts was low. Adherence to isoniazid treatment remains limited. Factors associated with loss of contact tracing were identified, which may guide strategies necessary to improve this process.