Our present government has shown us that knowledge of facts is unnecessary. So test literacy and numeracy both written and oral. I do not know enough about science to say where it fits? Humanities via a written/oral paper. And the rest by competency. e.g. I chose art and after a term find that I cannot hit level 1, I can change in the vague hope of finding something I can do!
The exam period would therefore be 3/4 days, one each English and Maths; 1/2 day for each of humanities, Then maybe a Science or sciences block? Schools would save thousands in exam fees. Competencies could be teacher assessed with some moderation. Schools would also save on invigilators and be able to run the normal curriculum for longer.
Add in things like attendance and employers would have a better gauge than at present. Students would be better informed about the future paths to take – University or Apprenticeship. The present system results in too many wrong decisions based on poor facts, by both students and higher education facilities.