Have you read the No Cry Sleep Solution?
This might be a good first step before you go to sleep school. Sleep schools do use 'controlled crying' which is just CIO. Reading this book will help you figure out a 24 hr plan, and will highlight the reality of sleep. Are you nursing? Is your DS close by, or at the other end of the house? Are you keeping a solid night routine?
Also, 3 naps of 1-2.5 hrs during the day is on the high side. You might want to try working down to 2 naps a day instead. If your LO takes 3 naps (1 hr, 1.5 hrs, 2.5 hrs) that = 5 hrs of naps. When is that last nap? How long is it for? A late, long nap could really muck up night sleep for a 6 mth old.
Anyway, I hope you find some rest