Tricky one to advise on this - IF what is being taught comes within the exemption you mention (presumably section 6 private tuition?) then all well and good and i would say the following.
I am also presuming this whole class is done by the one person with "no helpers"
as you say the higher turnover could flag up a vat enquiry - it would be silly if it didn't at least raise a flag.
(1) Put relevant notes on the self assessment return to indicate that turnover includes x amount exempt income therefore turnover below vat registration threshold.
(2) You can write to vat office to get written clarification / support for the view that the relevant turnover is exempt from vat if you have any doubts - you should put full details in with regard to exact "nature of services provided" and ask the direct specific question ideally with reference to the relevant section in the vat manual. If there is any other evidence you can find attach that
However i personally don't know enough on the finer points of section 6 to advise in this regard as to whether exemption applies which is the main question - i wouldn't presume it isn't ok but i wouldn't presume with 99.99% certainty the other way either. unfortunately. time for a cop out with posting of link
- are these classes educational or recreational? would be one thing lingering in my mind. Hopefully someone more versed in this area than me will offer some opinion in this regard.
If in doubt written confirmation from vat office as recommended above would be a good starting point.