eyebrowse, I disagree. The tests are just tests, and to some extent they are a test of how fast you work. Some dyslexic kids may do well enough to pass, but if your processing speeds are very slow you are likely to struggle. Our experience has been that dyslexic DD has done far better at school than any aptitude test has ever suggested. Her GCSE and AS results and A level predections are far better than the Tiffin average, yet she was placed 800th on the Tiffin wait list. Ditto her CAT scores were sufficiently bad that her Prep School Head, who apparently did not believe in dyslexia, took your view and suggested she did not apply for selective secondaries.
She has had the same experience with the medical school aptitude test where she did not get a great result, but was lucky to be accepted by two places where the tests are not used much in selection.
If a bright dyslexic gets through a grammar school test they have done very well indeed and should be fine in the classroom. My advice would be to practice, practice, practice as timing will be an issue. Also get some support for either english or maths if they prove a problem, as these are building blocks that affect access to other subjects.
We were lucky in that some private schools take a broader view when selecting and will take pupils with a spikey profile. And there was plenty of support in school.
I am so glad we did not listen to the Head, and essentially "give her a more fulfilling life", but instead keep doors open so she would still have choices at 16 and 18. My instinct was that she would want to go to the same sort of school as her friendship group, who were bright, purposeful girls. In DDs case at least, I was right.