The policy conclusion are clear:
If an objective of schooling is to increase women’s career opportunities and thereby their salaries, our results would suggest that gender-separated classrooms would be an effective step in the right direction. Gender-separated classrooms would increase the probability of choosing high-earning majors for both women and men.
Similar evidence, for university students, have been obtained by Booth and Nolan: "after eight weeks in a single-sex environment, women were significantly more likely to choose the [risky] lottery".
While the Italian evidence is from a "natural experiment", the evidence by Booth and Nolan is from an actual field-experiment, following an earlier study in high-schools. Good schools should offer students the possibility of choosing single-sex classes or offer the possibility of a random lottery over single-sex or co-ed classes. (Which provides additional data for analyses of peer-effects and subsequent outcomes.)