My DD is very bright, excellent vocabulary and reading age, great at logic puzzles, loves maths and science, very advanced in both cases.
She did not get the required cut off mark for local super selective (by 2 marks- I kid you not). I only put her in for one school too as I didn't want to pressurise her into doing lots of different tests.
I started informal prep in y4, got a weekly tutor in y5, did daily practice from Jan of y5 using cgp online tests, did one full practice test a weekend from summer term y5. We also did 2 mock tests at the school. The tutor thought she'd get in but she didn't!
She was competing against thousands of other girls, many of whom attended private prep schools and/or has more sustained tuition for a longer period of time. She was getting 80% on average on her test papers and the feedback from her mock tests said she'd get in.
BUT she is a September born so I had not factored in that the paper would be age to adjusted. She would have dropped marks because of her Sept birthday- bear this in mind, I wish I had. We actually had to aim for 90% really!
In the end, she got a place at a fantastic comp and loves it, and gets so much praise from teachers... which really boosts her confidence!