In Great Britain there have been school uniforms since the 1960 , and it has been a normal thing for everyone to wear when attending school.
The uniform is designed for which school you attend - it resembles the school. The uniform is a common sign for discipline, respect, order and equality.
At this point the parent of the kid is certain that the new headmaster is making a statement - he wants to strict the discipline of the school and heighten the respect towards him.
The advantages of having school uniforms is that it creates a unity between the students, it makes the risk of bullying lower and they are all equal.
It also makes the students aware of the meaning of discipline and respect for the place you are studying at, which prepares them for graduation and the jobs they will get afterwards.
It also gives them something to accomplish - if they go to a good and well known school - which often is schools that have a policy for uniforms due to the respect, discipline and weleducating historical legacy - get good grades and have a respectful school attendance, then they will have a good reputation and a very fine résumé when they are looking for jobs.