This will depend on the subjects your child is planning to pursue in Year 12 for A-Level or IB. Most schools will allow potential 16+ applicants to sit exams in three or four subjects only, rather than requiring specific subject-assessments. 16+ entry usually comes with a requirement for particular grades at GCSE, and these will be detailed on the school website. Check the
entrance requirements for the school to which you are applying; this will avoid disappointment if GCSE predicted grades are unlikely to match up to these. Additionally, there is often an interview, and occasionally a standardized Critical Thinking or Reasoning exam.