The IP allows students to benefit from a broader learning experience in both academic and non-academic aspects, with time freed up from not having to sit for a national examination at the end of Secondary 4. Hence, the curriculum structure and curriculum content is left to each IP school to design, and can be different from the national secondary curriculum. The IP culminates in either an A Level or IB qualification, so these students are also generally not expected to branch off to other educational institutions at the end of Sec 4.
Since this is the curriculum design and intent, G1, G2 and G3 are not relevant and SBB does not apply.
Nevertheless, it is important for students from IP schools to be able to mix and mingle with other fellow Singaporeans to understand that they are part of the wider society. IP schools will do more to enhance interaction between peers of different backgrounds and with different schools.