For my year 9 SATs I was given extra time, and I have been allowed extra time ever since. I am allowed to have 25% extra time in my exams, this will also be true for my GCSE exams over the next couple of years. This has been very useful as I read slower than normal because of Nystagmus. If you are worried about your exams I would go and see the Exam Officer or the Special Needs Co-ordinator at your school. For my AS exams i had to get a letter from my opticians to say that I take longer to read than most others, this meant that my school had evidence to support an application for extra time.