I think GCSEs are important since they are the first proper exams and the only time that the whole cohort does the same exams. However, they quickly get eclipsed by sixth form which, probably will be eclipsed by university. So, they are important but not that important.
I want DS2 to do himself justice, although right now I have no idea how good (or otherwise) he is. The KS3 monitoring reports were deliberately opaque.
Since it's my second time around, and I have only just finished seeing DS1 go through the GCSE process, I feel like I know what is likely to happen.
As a general timetable, I think it goes:-
Year10, Christmas term: get a school report that gives aspirational target grades. Try to make sure DS2 keeps his notes in order and encourage him not to leave any topic without having learned it. Don't read too much into end of topic assessment grades because they will change.
Year 10, Easter term: same as the first term, but start DofE stuff. Maybe sign ds up to Seneca or get him to watch some MrBruff videos.
Year 10, Summer term: end of year 10 exams. Make sure DS takes them seriously. Treat them like pre-mock, mocks. They are a good chance to help DS work out what revision techniques work for him.
Year 11, Christmas term. It starts off feeling like year 10 but ends with mocks in either January or December. These feel like a real effort but they are only the warm up. Get thematic desk, chair and a place to store their study materials, if you haven't already. Also get a full set of revision guides. Start planning which sixth form to go to and which A levels to take.
Year 11, Easter term. Things are getting serious. It's time to put a comprehensive study timetable together and for DS to start balancing his time between work, rest and play. The school's extra revision sessions start kicking in before and after school, but typically they are targeted at those who most need them ( optional for everyone else).
Year 11, Easter holidays: hard work and an endurance test (for both parent and child). Suddenly the maturity starts to show and your little boy is gone, replaced by a near adult who can do so much more than you thought they could.
Year 11, first month back after the holidays. Teachers who haven't finished the curriculum are in panic mode, and every class is a revision class with past papers galore. It begins to feel like time is running out and it is necessary to prioritise what is still to be learned. If there has not been enough revision by now or it hasn't gone well, then there is a tough realisation that it's too late to catch up completely and that will be reflected in the grades.
Year 11, mid-May the first GCSE. Parents panic that their DC will remember to leave their phones outside the exam room. The rhythm is: sit exam, come home, see the funny Twitter memes where everyone says they did badly, tidy away the revision stuff for that paper and get the revision stuff out for tomorrow's paper. Repeat for a fortnight.
Year 11 Summer half term. More revision.
Year 11 June: last couple of weeks of exams, then chill!
Year 11 July: school prom
Year 11 August 23rd go to school and get the results.
It goes really quickly!