I learned a few days ago my sister-in-law, a public school librarian, has taken on an after school assignment teaching students English in preparation for college. She told me her assignment is difficult because the district is poor and the students she's teaching aren't starting at expectable grade level English skills.
I also learned she has her PhD and one of her specialties is designing course instruction. I have no doubt she'll do an excellent job.
My guess would be, generally, even without having been a teacher, that the more a teacher expects, and the more rigorous a teacher is, at any grade level, the better the result will be.
For my part, I told her about my experiences in grades 11- 16, she kindly compared me to my sister (not quite warranted in all humility) and of course I said thank you.
Teaching, tutoring, and mentoring are essential. I myself would probably sound like and have the communication skills of a caveman it hadn't been for my luck in having a mother who taught me how to read and write and great teachers who had the resourses to do their jobs.