Yes, historically there’s been a better than 90% chance of getting in to CCA through the lottery. In this year’s lottery (for next 2013-2014 school year), it was reported that there were 138 who did not get in. Since total enrollment is a little less than 1900 students, that equates to about 7% if I did my math correctly.
Students who have a sibling at CCA are guaranteed a spot, but only if both siblings would be enrolled in the same school year. For example, families who have an 8th grader wanting to enroll at CCA next year as well as a graduating high school senior do not gain any advantage for their 8th grader/potential freshman. But if your kids are close enough in age, it works out nicely if the first gets in and the rest want to follow.