Hi!
I went to tutoring for Selective schools and definitely got into a good school. But looking back, I realise that I wasted so much money on tutoring, because I never did my homework! I just turned up to lessons and hoped for the best.
You don't need to go tutoring for content but you do need help with exam technique and exam-style questions. If you don't want to go to tutoring, buy some books with practice papers/questions. Understanding the exam format/layout is a major way to stay confident during the real exam!
I'm not going to lie, everyone that I've seen so far, who've gotten into good Selective schools, have gone to tutoring. But how you utilise tutoring is the most important thing. Like I said, I went every week, but NEVER did my own homework. How I did so well is a mystery to me...
I know some places offer Selective 'crash course' style preparation, where tutoring is only offered in the holidays, or in the weeks leading up to the exam. Maybe you should consider this style of tutoring.
Otherwise, practice questions and ask your teachers, parents, older siblings or friend's older siblings for help!
Hope this was helpful!