This article explores the relationship between school choice, student mobility and school segregation in Barcelona. The case of Barcelona is particularly interesting because the school admissions policy combines a particular design of catchment area with a significant level of choice options. We work on students and school register datasets for the school year 2016-2017 to observe the association between the socioeconomic characteristics of the students and their residential and educational geographical distribution. The article tests whether recent reforms that have undermined the role of residential proximity in admissions policy have impacted on the school segregation of three groups of socially disadvantaged students (foreign students, students entitled to Free School Meals (FSM) and students who are Recipients of Social Allowances (RSA)). We explore different patterns of mobility between socially disadvantaged and non-disadvantaged students and the impact of opting out from neighbourhood schools on school segregation. By using a counterfactual approach that compares real enrolment with simulated school enrolment in proximity schools, we provide evidence of a significant reduction of school segregation for all socially disadvantaged students, showing the negative effects of the current high number of school choice options. In addition, our analysis shows that school choice boosts remarkably the inequality between public and private subsidised schools. The final section of the article reflects on the implications of our findings for potential reforms in the current definition of catchment areas and the overall school choice policy in Barcelona.