Do your homework
It is my understanding that Fairwinds Sailing School has had issues with both ASA and US Sailing so they needed to fabricate their own sailing certification to offer students. I have never heard of ICSO until now and did some research. I would agree with FarCry that the instructor is everything. Do your homework as there are MANY schools out there that don't offer quality even if their website looks impressive. If you desire certs, ASA and US Sailing are practically the same. Maybe start with schools or instructors who have won national awards or something.