If you think you can get an average 13-year old ready for college-level CS in one year, without sacrificing the rest of their usual middle school and high school education, you're severely deluded.
First of all, they're not trying to teach "average" 13-year-olds; they're trying to teach 13-year-olds who've applied to a special magnet school because they want to be software engineers (and presumably have at least some aptitude for it). That's a very different demographic.
Second, I coasted through my college intro to programming class (and the data structures / object-oriented programming class after that) on what I had taught myself back in middle school and high school. Anyone who can't do at least as well with a year (or less) of actual, dedicated instruction is completely unsuited to the field.