To be awarded teacher certification in England you need to be registered with the General Teaching Council of England (GTCE). However, overseas teachers from non-European Economic Area countries--such as the USA--also need to apply for sponsorship, work permits and additional training. All overseas teacher training is handled by the Training and Development Agency for Schools. You will need a college degree and ideally some teaching experience before applying for certification to teach in England.
Apply for a teaching post at an English school. You need to find a school listed as an Employment Based Initial Teacher Training Provider (EBITT). This will allow you to teach while training for full UK certification. The TDA website has a list of EBITT providers. It's also worth checking for vacancies via UK national newspaper listings, such as the Times Educational Supplement.
Accept your job offer. Confirm with the school that you intend to train as an overseas teacher and require them to sponsor you to work in the UK.
Complete a GTCE provisional registration form for overseas teachers. You can find this on the GTCE website. Once you have added your information, pass the form to your school in England and ask them to enter the relevant details.
Register for a work permit via the UK Border Agency website. You will need to provide confirmation of your sponsorship from your English school.
Fly to England and start teaching when your employment date begins. Liaise with the TDA to continue training for your Qualified Teacher Status (QFT) while you're on the job.
Finish your QFT training and apply for full registration with the General Teaching Council of England. If you're accepted, then you're officially certified to teach in England.