I had a tutor at A-Level for a language following difficulties with my teacher who ruined my confidence at oral work by ranting at me in front of the class on several occasions. It didn't help that I was also having difficulties with ear infections/ perforated ear drum which the teacher dismissed when it was relevant to some of my difficulties.
The tutor was great at getting my confidence back to where it should have been by giving me a "safe" environment to work in. Although my eventual grade wasn't high ranking, it was definitely better than the predictions of gloom from my teacher, and I had the satisfaction of it being a fair grade.
The only downside was that it looked better on my teacher than he deserved (although my lovely co-teacher would have got a little credit although it wasn't her side of the syllabus we were working on). At least I got some satisfaction the day that I came in with the consultant's letter advising that I should have earphones for the listening exam rather than listening on the stereo with the rest of the class- so much for the "non-existent" ear problems that I'd had for many years 
If I felt that my DCs were struggling with something specific that could be assisted by a tutor, then I would get a tutor. The advantage is the specialised angle of the subject knowledge, and being more attentive than they are with the familiarity of a parent.
At least tutoring for 11+ isn't an issue for this area, that's a separate issue to me compared to boosting personal exam performance or specific difficulties.