Alternatively, I think a better solution is to make these tests untimed for everyone (or double time for everyone).
Tests are timed for a reason. A student that knows the material well is likely able to answer the questions more quickly than one that does not (LDs not included). Should one kid have 6 hours to do a test that is designed to last one hour? There are kids that legitimately need more time and who have processing speed issues. It is equally true that poor kids of color are much less likely to be identified as having LDs than wealthy white kids. It is also unclear how the added time is determined. Every kid with xyz LD gets an extra hour?
I remember a neighborhood kid who had pretty significant ADD hyperactive. He had previously gone to school in an urban area and was not diagnosed there. Not until he came to a "good" school was he IDed. And that was a white kid with educated parents.