There are a number of international qualifications around and it is important to know the differences between them. I want to state that all of these qualifications are highly thought and any one of them will help you on your route to university.
iGCSEs taken at 16.
Let us start with iGCSE. iGCSEs are the international version of the GCSE, which students in the UK take at the age of 16. These give teachers and parents a good idea of how well a student might do academically. In the UK at least a C in Mathematics and English is a must for most employers. iGCSE grades are taken into consideration when applying for university and will help the university to decide what conditional offer to make. It is expected that most students will take iGCSEs and it can make if your child has NOT taken iGCSEs it may mean you have to delay your application until after they have either their A-level or IB results.
It is possible in some circumstances for you to enter a university foundation programme straight after your iGCSEs, but many programmes need students to be 17 to enter such a programme.
IB Diploma Programme suits All-rounders
Many schools offer an IB Diploma programme which is widely respected and offers a very good all round preparation for university. It means that students do not have to limit their choices so much at 16 and suits students who are all-rounders. If a student can handle languages, science and the arts then this could be the best option and is able to write large essays independently then this could be the best option.
A-levels enables earlier specialisation
A-levels originate from Britain and students choose 3-4 subjects, it is up to the student how balanced these are, but if your child definitely wants to do science then they can do so, if your child is not good at languages then these can be avoided etc. On top of the 4 A-levels students can choose to do an extended project, which is similar to the IB Extended Essay.
Both are accepted world wide and although in the UK A-levels are the more common qualification universities are happy to make an offer based on IB results. (These offers have improved in recent years as universities gain more experience with the IB qualification) Australia have tariffs for both qualifications and it is a simple matter to apply.
However if you are intending to go to the US there are some other considerations. Many US universities require SAT exams to be sat (https://collegereadiness.collegeboard.org/sat) and you will need to make time for these. Also currently if you take modular A-levels you may get unconditional offers from a US university based on your AS-level grade.