My son took the ACT as an 8th grader and scored a 19. What is his projected 11th grade ACT score? How does his score compare to that of other 8th graders, nationwide?
On average, 8th graders score about 7 points lower on the ACT than high school students do, so your son's projected 11th grade ACT score would be a 26.
As far as other 8th graders go, your son is above average - the average ACT score for an 8th grader is a 13. In fact, his high ACT score would qualify him for several different programs at Duke TIP and CTY at Johns Hopkins. Depending on his section scores, your son could qualify to take eStudies online courses through Duke TIP, CTYOnline courses through CTY, or Academic Explorations summer courses through CTY.
Even if your son doesn't end up participating in any of these extra programs, though, he can rest assured that his ACT scores are as good as or better than 75% of all 8th graders.
Source: Dr. Fred Zhang's analysis and quantile matching of Duke TIP and Johns Hopkins CTY student data (the article summarizing these findings can be found here).