This article explores the effects of charter schools on teachers' working conditions in Bogota (Colombia). By employing a semi-experimental approach involving Propensity Score Matching (PSM) and Difference-in-Differences (DID), we find that in the close vicinity (postcode area) of where they are established, charter schools more than double teachers' workload for a comparatively small increase in salaries. In light of a neo-institutional approach, we argue that those advocating for the diversification of school types in Colombia have decoupled the presumed benefits of charter schools' competition from their actual negative effects for teachers. Moreover, we also point out that despite charter schools in Colombia (Bogota) having a not-for-profit status, existing labour flexibilisation policies have exerted isomorphic pressures on them, forcing them to adopt short-term contracts and thus leading to ravaging competition practices among teachers. Overall, we contend that the introduction of charter schools in Colombia (Bogota) has led to a general precarisation of teachers' working conditions.