I retired last year from more than 20 years' one-to-one tutoring for 11+ entrance to both state and independent schools. For the last 10 years of that period I recommended that parents enter their children for chuckra's mock tests.
I found that this served many purposes; firstly, children from the maintained (state) sector, usually have no experience at all of formal exams or of examination procedure, which puts them at a disadvantage compared with children from independent primary schools who are often more used to a formal exam setting. Just taking a chuckra mock test gave them that valuable experience of sitting in an examination room, listening to instructions, learning to disregard other entrants' rustling of papers, sneezing, coughing, wriggling etc. and watching the clock to see how much time they had left. Secondly, it gave the complacent ones a 'wake-up call' and the anxious ones reassurance that the tests were within their capabilities and we'd been practising the right skills! Thirdly, I found that if children repeated the tests a few weeks later, they almost always did better second time round, which was a huge confidence-booster. One year I was dismayed to find that one or two papers had been less-than-carefully marked, but generally I was very happy with the whole set-up. I think the mock papers were slightly more difficult than the actual entrance papers my pupils sat (for Reading, Kendrick and independent schools in the Reading area) but that is a good thing.