As they'd only just have started S1, I don't think they would need any certificate. Even in those schools that "set", most only do so once they've assessed the pupils themselves and don't rely on the reports from the primary schools.
I know at Shawlands, they set Maths quite early, certainly by the September Weekend - but then it's relatively easy to assess via tests. English took a little longer - until after the October Week. Those are the only two classes that they set - the rest are all mixed ability, I think until S3 (which is when they've started to choose specific subjects to take forward to Nat 4/5s). Not all schools set though and some schools may stream rather than set.
Re the Curriculum for Excellence, Glasgow seems to have left it up to the schools how they choose to implement it. I'm happy with how Shawlands is doing it. They're being allowed to choose on a subject by subject basis whether they do "old" or "new" Highers next year - and some subjects are choosing new because they say in some subjects it is so strongly correlated to what they've been studying at Nat 5 (and prefer the new qualifications), whereas others have preferred to stay on the old Highers for one extra year.
Ds' S2 English class is currently doing Nat 4 pieces of work (he's just done a "Personal Writing" essay which was one of the few that he's let me read and it was very impressive - but wouldn't let me touch or comment on as to him, it was the equivalent of an exam).
I've heard mixed views from friends in East Renfrewshire on its strategy of only doing the old qualifications for another year. Some parents are concerned that they're just delaying the inevitable and not putting in the preparatory work (or expecting other schools to do it for them).
As an aside, I don't think we took any report to NZ when we went (beginning of S2 for me but this was c.40 years ago 
) - but when we came back, I got the BEST REPORT EVER from my NZ school according to my headteacher who had to sign it off and my dad forgot to pack it into our "staying with us" luggage 
. Fortunately, we went back to my old school, so the teachers had a sense of what I was capable of and took on trust that I should be in the top sets 