Rita Bavaria is a whole different world. My sister is 29 now. However, she finished Realschule at 16, then completed her school-based vocational training for three years, worked for a little while, started her undergraduate course (she's a physio)...completed that as a 2-year short course due to experience, worked a little more and is now doing her MSc in Health Management (part-time, while working).
My parents operate very much along the lines of: "As long as the child is happy, who cares?" Our grades were mostly between 1 and 3, sometimes a 4 or 5. They didn't stress much about it and always went on the premise that their children are actually bright, but need to find their own way in life. School's important, but it's not everything. (I do appreciate that this is a very unusual approach, particularly in Western Germany. Most of my friends' mums were constantly hovering around them.) We were one of the few families, where both parents were working full time, so there certainly was no time to constantly do extra work or taxi us around to enrichment activities. (They did sit down with us and help/explain, if we asked for it.) It's something I try to instill in my classes here in the UK - to take some responsibility for their learning. I'm there to teach,...I can't make them learn. That's fully up to them and won't work unless they are prepared to do it and are ready to put the effort in.
sunshield There are different types of Gesamtschulen. In some, you get set across different subjects, similar to British comprehensive schools. In others, you are basically in a stream and stay there. Classes don't tend to mix and lead to different qualifications.
We didn't have to take a test to go to the Gymnasium. It was purely based on grades and teacher recommendation, together with parental preference. (Rules depend on the federal state, though.) Children, who do not speak German, will struggle in both Gymnasium and Realschule. That's why they usually get put into the Hauptschule - at least initially. A friend of mine came over from Eritrea and repeated a year in primary school, to get the appropriate language skills. She then moved up to Realschule and Gymnasium - thanks to her very pushy social worker. However, as a parent, you need to push for it. Nobody will simply move them up.