I am an adult who was diagnosed with Asperger's in 5th grade.

How old is your kid? If they are as high-functioning as you claim, then you should involve them in the decision-making about what to do. ("Do you want me to tell your teachers you have autism?", "Would you like plain food at school?", etc.)

When I was in school, the written "Individual Education Plan" said that I got an extra 30 minutes per hour on tests. In practice, this starts a conversation between the teachers that says, "this student needs special handling for tests". In practice, the accommodation I requested (and usually got) was permission to walk out of a test or exam as soon as I finished (sometimes half an hour early).