in Scotland, the year a child starts school is determined by the year of birth, and they will start formal education between the ages of 4.5 and 5.5.
Eg if your child turns 5 between 01/01/15 and 28/02/16, they can start school in August 2016. Those who turn 5 between 01/01/16 and 28/02/16 can start in August '15, but they don't HAVE to start until Aug '16.
They go into Primary 1, full time at this time.
Primary school last for 7 years, ending when they are 11.5-12.5
They then go into S1.
Secondary school lasts 6 years, from S1-S6, so ages 11.5/12.5 -17.5/18.
Depending on when their birthday falls, they can leave from the end of S4 onwards.
As for individual schools, I can only speak about Dundee, as that's where my experience is.
I have a dd who is 17 in S6, and ds who is 12 and in S1
There is only 1 private school in Dundee, the High School of Dundee (or Dundee High as it's known), which is a co-ed day school covering primary and secondary
If we'd been able to afford it, my children would have attended Dundee High, both because of the smaller class sizes and the ethos of the school (social issues there are exactly the same as at pretty much any other school)
There has been a huge amount of change in the schools in Dundee in recent years, and not always for the better.
I live in Broughty Ferry, which is the catchment area for Grove Academy, which seems to be one of the most sought after secondaries due to good results. You'll note I'm not saying it's the "best" although I believe it has the highest exam results in Dundee, as it's become somewhat a victim of its own success in recent years, and despite a brand new building 6 years ago, is now bursting at the seams due to out of catchment area placing requests.
The 3 primary schools in Broughty Ferry are also "suffering" similarly.
Do you have any specific things you want to know? I could ramble on for long enough but not tell you the one thing you really want to know!