There are multiple ways but the easiest is by using a proxy. You should be aware that schools do block the most popular web proxies but if you can find one that isn't then your home free. Here is one you can try: www.sl.404-fnf.com
Someone went on it a our school an they got in big trouble. The surver that blocks it would send the someone got on it and what computer it was from and the time. So you would get in big trouble from your school.