Article errors in formal writing: how much do they drop your band score?

Many Korean speakers drop articles because their L1 does not mark them, yet in Task 2 essays this often shifts from precise to vague reference and lowers the score for grammatical range. The rule itself is simple once learned: use "the" for shared knowledge or specific nouns and "a" for first mention of countable nouns, and the pattern stays corrected after deliberate practice at 250 words per essay. I wonder whether drilling articles and prepositions first would raise more scripts from band 6.5 to 7.5 than focusing on new slang.