The start date for any student is always a case-by-case decision by the Head of Division. In theory, your child can begin school as soon as the admissions process is completed and a place has been offered. Practically speaking, however, a student will not usually enter ECC, ES or MS after May 1. High School students are not usually accepted after the beginning of the second but each application is looked at on a case-by-case basis. The Admissions office will contact you with the specific starting date.
IB Diploma students: If the student is not already enrolled in IB courses that are transferable to ISB, it is not possible to begin after the beginning of October.