We have a Parent Information Evening in mid January (which was apparently very similar to the School Assembly on the same topic) for the S2s & S4s and their parents, explaining the choices, columns and routes through to Nat 4s or 5s and then on to Highers.
It is combined with a Careers Event which the Parent Council helps organise (the S2s & their parents get their talk while the S4s go round the representatives from a selection of possible careers and/or local Unis/colleges/apprentice providers, then they swap over).
The Senior Management Team are very visible at this (and at Parents' Evenings) and Pastoral Care teachers are also there - and at the Parents' Evenings.
The pupils make their choices in S2, to allow the school to present pupils for 8 Nat 5s (those that are capable, of course) and they start their S3 timetable at the beginning of June (which iirc takes them through to their exams in S4).
There is an S2 Parents Evening about now (was supposed to be last week but got postponed because of the snow) so that parents get a chance to talk to their kids' subject teachers (ds' Modern Studies teacher was really disappointed to be told in S2 that ds wasn't going to do a Nat 5 - but he got him back in S6 for a crash Higher
) before they finalise their choices.
But there are also two school reports sent out over the school year: an interim one with less detail and a detailed one later in the year - which also have space for/expect a response and where you can ask any questions. The booking system for the parents' evening also has the opportunity to ask any specific questions in advance with each teacher with which you make an appointment.
It must be frustrating for you if you never get a response. As someone once said to dh, "A message is not a message until it has been received and acknowledged" 
Not really sure what to suggest to you: join the Parent Council and get to know the SMT? Although the Parent Council itself will not get involved in individual cases, it does have a wider role of discussing school policy (so things like setting and encouraging that a policy of "equal stretching" rather than "rounding down" would come into that), as well as communication, response times and representing the wider Parent Forum. It also provides the opportunity to get to know the head teacher and his/her challenges.