There are two types of flight schools--FAA-approved and non-approved schools, depending on whether they comply with federal regulations. Non-approved schools offer more flexibility for students in terms of their lesson plans and scheduling. But if you want to fly for an airline after graduation, you should check out the schools thoroughly and try to meet the requirements for entrance into an FAA approved institution.
Additionally, The Transportation Security Administration (TSA) requires flight schools to verify students' proof of U.S. citizenship. If you are a U.S. citizen, you must present a valid United States Passport. If you are a foreign student, you will need to call the school to see if you meet the specific requirements.
You must have a high school diploma. Some schools require at least an associate's degree, but not all. Some airlines will not hire you after pilot school graduation without a college education. In some cases your flight training may count toward some credits for an aviation degree.
Depending on the school, you may be subjected to a background check, credit check and drug test. You will have to pass all these tests, however, to be employed by an airline later. Most schools offer financing--it can cost between $30,000 and $50,000 to attend.
FAA regulations require that your vision be correctable to 20/20. So even if you attend a non-FAA approved institution that does not have strict vision requirements, you will be considered unemployable by most airline standards if you cannot correct vision to 20/20.
Take flying lessons before going to pilot school. You may want to consider trying it to see if you enjoy it and have an aptitude before investing. In the United States, you can fly as early as high school. The more flying hours you have, the easier the flight certification and flight simulator will be in flight school. Also, the admissions department may look more favorably on your practical experience.