There are 2 AEIS exams each year. One in Feb and another in October.
For most private schools, IELTS score isn’t considered as a must when they proceed for the application. They can either choose to do the placement test with the school or submit IELTS score to get exemption for English studies.
International school follows IB syllabus which is mainly designed for students that would like to further their studies overseas. IB syllabus is good for student’s future transfer to U.S., U.K., Australia etc.
Private school is another type of education system in Singapore. They either provide preparation course to help students enroll government school or provide higher education with the collaboration with third party university in other countries.