If you have decided to do 11+, then some form of preparation is likely to be needed.
These days, especially in the areas where there are super selectives (Grammars with no catchment area and no pass mark, just the top X number from perhaps sleeve rail thousand applicants getting the places) being clever alone, isn't enough to get you in. All of those plus lots more will be very clever, and those who get the extra couple of marks which get them the place are also very speedy and accurate, which comes through practice. Of course, many Grammars a not superselective and in those areas, being in the top 20-30% may be good enough rather than the top 5%.
Even in the fully selective countries like Bucks and Kent, most people getting Grammar places do some preparation. However, Tutoring can mean many things and it might involve a paid person, but can just as well involve a parent. The key thing is that the child is sufficiently familiarised with both the content of the tests in the relevant area, the styles of Qs and the speed needed. Paid tutors can clearly do this, but there are also loads of materials available for free or purchase which means thousands of parents do it every year too.
For a parent to do it successfully I think;
- they need to have time to put into it - for researching, reading up and then delivering
- they need to have the confidence that they can do it and that they can work productively with their child
- they need to be resilient - because it's not always an easy process.
Having said these things, lots of people think parents can be the best tutors, because their level of commitment to their own child is always higher than that of a Tutor. They can be flexible and work with their child little and often.
However, lots of people choose to pay. They might not have the time to research and deliver due to work or other family stuff, they may not be confident that they can successfully deliver the material or think their child won't be co-operative if working with them and it will damage their relationship. they prefer to use someone who has experience of the process.
At the end of the day, it's a personal choice and there isn't a right answer. Equally there isn't a right answer as to how intensively a child is prepared. Some people do a full 2 years and others say 6 months is enough. Others just do a few weeks which is little more than making sure the child has seen past papers so knows what they look like. However, to so absolutely nothing is a mistake. If the first time you see non verbal reasoning questions is the day of your 11+ or have to spend valuable time grappling with what questions mean because you sent familiar with the terminology or paper or answer sheet style, then a child is definitely disadvantaged.
The 11+ exams forum is very detailed on all of this and has sections devoted to different regions which might be useful to you. Do t be put off by those who are zealots of the 11+ and everything related to it - there is loads of great advice there and many people who have been through the process share their wealth on info in order to make the process smoother for others.