Have a think about Shawlands Academy. Despite a very diverse catchment it gets good results.
It does seem to encourage confident youngsters: one of its pupils ended up being an ambassoador for Glasgow's bid to hold the Youth Olympic Games in Glasgow unfortunately Buenos Aires won it , it does Duke of Edinburgh up to Gold Level, as well as things like the John Muir award in the earlier years.
Ds is in S2 and is being stretched in both English and Maths (he's in the top set for both - they are set from early in S1): in fact, in English he is currently mirroring what the S4s studying for National 5 are doing as his teacher thinks the class is capable of it (I have my concerns, even though English is my strong subject, as I also want to be sure that he learns to love English and if she pushes them too hard and too fast....
).
It is also an SRU funded School of Rugby, which doesn't mean that you have to be good it, but those kids who are in the "Rugby Class" do extra rugby, fitness and nutrition and are supposed to be exposed to the discipline and values that form part of the rugby ethos.
Not sure what it is like for Arts - ds is not particulary arty or musical (to my chagrin) - but the facilities seem good. They do the same subjects in S2 ans they do in S1 (which includes blocks of Art, Music, Drama, Tech Drawing and Home Economics) and then begin to specialise in S3. Shawlands allows them to study for 7 National 5s (plus an extra "fun" interest such as PE or Drama that might just be taken to National 4) - which apparently not all schools are doing. Likewise, it is still allowing them to all 3 sciences for National 4/5.
Last year 20% of S5s got 5 or more Highers.