The issue of school uniforms is one that crops up quite regularly in the news. Uniforms are still common in many countries, although styles vary widely, and they have a lot of supporters. On the other hand there is a lot of opposition, too. If you're planning an essay opposing the use of school uniforms here are some arguments you can use.
Many school uniforms are designed to be affordable, but even so they become a significant cost when you have to buy them for two or more children. There's also the problem that children are growing rapidly, so a new uniform will probably be required every year or even more often. They don't even save wear on normal clothes, because those clothes will probably be outgrown before they wear out anyway, even if they're also worn for school.
Often uniforms include custom-embroidered items such as shirts or blazers, and many schools have a preferred supplier for these. In many cases there is only one supplier authorized to sell the school's logo. A large school can represent a significant market, possibly running to thousands of uniforms a year, and it can be tempting for a shop to come to an "arrangement" with a headmaster to become the approved supplier. This has happened several times in the UK.
School uniforms, especially for boys, have traditionally included a tie. There are risks from ties, though; they can become caught in things, creating a strangulation hazard, and are easily grabbed during playground scuffles.
It's often argued that uniforms reduce bullying by ensuring that all children are dressed to the same standard. It's a poor argument though. If children want to bully a classmate they will, no matter what he's wearing. If they can't tease him for his clothing they'll simply find something else.
By forcing children to dress identically their ability to express their personality, creativity and personal preferences is stifled. This is especially harmful during as important a formative period as school.
Uniforms often exclude items that may be important to a student's religion. There have been many cases of girls being suspended for wearing veils or jewellery that violate a uniform policy but are required by their religion.
It's obvious that there are a lot of things you can say against school uniforms. A quick web search will find lots of blog posts or articles on any of these topics, so it will be easy for you to collect all the information you need to write an interesting, persuasive essay.