My 7th grade son took the ACT with Writing and got a 18/36 on the Writing section. Is this score above average?
Because the new ACT Writing scoring scale is so new, it's difficult to say for certain where your son's score falls. My best estimation is that an average score for high schoolers on the new ACT Writing is going to be around a 20 or 21 out of 36, which would make your son's essay score above average for his age.
Sources: Dr. Fred Zhang's article on what a good 7th grade ACT score is as well as my own research into ACT Writing scoring (more on average ACT Writing scores here).
UPDATED ANSWER: Yes, an 18/36 is an above-average ACT Writing score for a 7th grader. Based upon the information ACT, Inc. has released about percentile norms on the new ACT Writing, the average ACT Writing score (for all students) is between a 16 and a 17 out of 36.
Based on analysis done by PrepScholar co-founder Dr. Fred Zhang, we know that 7th grade ACT scores are about 10 points lower than those of a high school student. While the scoring issues with ACT Writing make predictions a little more difficult to make, I feel confident in stating that an 18/36 is an excellent ACT Writing score for a 7th grader (considering it's above the average ACT Writing score for all students, including high schoolers!).