S1 was at a STEM HS, S2 was at an IB program. S2’s freshman year pre-IB English was more rigorous than S1’s junior year AP Lang/Comp. They were both reading many of the same books that year – S2’s essays were far better, and he got B/B- grades. S1 scraped the surface and got As. S1 never had to write a lengthy essay or paper in HS, other than his STEM research report. S2 did nothing BUT write long papers in HS, and the programs he was in prior to HS also had a research paper each year, starting in 5th grade.
If the English classes are so poor, perhaps your S would consider getting involved in the school paper? A friend suggested this to her S in lieu of attending the IB program and he wound up becoming a successful comedy writer. Journaling might also help with growing comfortable with expressing ideas, parsing an argument, working through a block. National History Day is also an opportunity for developing research and writing skills.