Ditto to aculady's response. My ds12 has dyspraxia, and has an accommodation on his IEP that specifically states he has the option for oral response on fluency tests.
In our ds' case, the school preferred oral response over extended time for fluency tests; he also has extended time accommodation on other types of testing.
polarbear
ps - if the teacher is disagreeing with an accommodation or has a different interpretation of what is meant by it than you do, you can call an IEP team meeting to clarify (we were sometimes able to do this type of "IEP meeting" over the phone if all parties agreed to what was going to be amended in the IEP). In this case, I think it might be beneficial to request an accommodation specifically for fluency tests.
