My ds is in S5 and my experience (of a whole one child
) to date has been positive - both of CfE and of the primary and secondary school he's been at.
He's been stretched and stretches himself.
His secondary school - within Glasgow, highly mixed demographic (from millionaire's kids to kids from highly deprived areas who literally don't know where their next meal is coming from never mind buying a scientific calculator), multiple languages (54!
) - is proud of its diversity and gets excellent results with a very high proportion going on to Uni/FE.
It does allow 8 Nat 5s (and ds got excellent results) and again, its results for those getting 5 Highers in a single sitting are good. It also offers lots of Advanced Highers (easier when it's a bigger school).
But as others have said, it really does come down to the school. In some cases there is prejudice and preconception - people moving out of Glasgow into East Ren because the results are "better" without checking out the local schools and seeing what they do in terms of the value add for individual children.
I went to a "good" school in a leafy suburb to the North of Glasgow (equivalent to the East Ren schools) and I would argue that ds' school is a better school as it is more inclusive (my school just cared about the academic kids - ds' school cares passionately not just about the academic kids but about the middle and low achieving cohorts and also encourages wider interests - ds is very sporty as well as being clever)
Ds' school, which has a good reputation, to date has been able to accept all placing requests - although I think it is getting near capacity.
Re the number of Nat 5s, while ds' school allows 8 (as Glasgow left the decision to individual schools), I have heard a depute from a different authority which restricted the number (to 6?) justifying it in terms of "Pathways" and ensuring that all pupils were going to get the results that they needed for the career path they wanted and that there were lots of enrichment options around the smaller number of Nat 5s.
In any event, all schools are "judged" on the proportion of pupils that get 5 Highers, so that remains important.
Via ds' rugby club (not one linked to any private school
) I get to talk to lots of parents (of girls and boys as there is a strong and growing girls' team) both at ds' school and at other schools in the area and they are all happy with what their school is doing for their kid. There is a range of academic abilities - from those who're expected to get/have got straight As to those who are not so academic but are still being encouraged to do well.
Good luck with your decision.