This study examines the causal effect of tracking postponement on higher secondary school enrollment in Italy, focusing on the impact of Law No. 1859 of December 31, 1962. The reform replaced the previously elitist lower secondary system, composed of multiple tracks, with a unified program known as the Single Middle School, aimed at reducing educational inequality. Using a Bayesian structural time-series model, we estimate the counterfactual enrollment trajectory in higher secondary programs in the absence of the reform, leveraging historical data from the ISTAT time series database. Our findings suggest that the reform significantly increased enrollment in one of those high school programs, the licei scientifici, while having little to no effect on the others. This increase may have been driven by the absence of barriers, such as Latin exam requirements, and the broader university access provided by the licei scientifici. Overall, the results indicate that postponing tracking accelerated an ongoing trend of increasing upper secondary school enrollment, likely enabling previously excluded student groups to pursue higher education.