The schools with ISC syllabus have their own eligibility criteria for admission into science or commerce stream or whatever.

Generally,in most of the schools the average marks required in science is 60%.They even check your mathematics marks as ISC contains a lot of mathematical relations in Physics and Chemistry.So,you need to be thorough with them.

Some of the schools with ISC are : 

• Garden High School,Kolkata
• Vivekananda Mission School,Kolkata
• St.Joan's School, Kolkata
• Calcutta Boys School
• Ram Mohan Mission High School

So it is better to interact with the school for admissions as every school has its own eligibility criteria.

All the best!