(It's hard to offer advice when the details aren't quite clear, but...) If you're teaching in elementary public schools, then (drawing on my experiences of them in Japan), I'd say it would be ambitious indeed to be expecting students much below the final year (or at most two) to have studied the alphabet (English ~) symbols and strokes much, let alone be 'able to write a complete sentence' or even words - letters would be about all I'd hope for (and even then, there might be quite a few b's for d's and vice versa etc).
In further relation to written answers, you might like to supply multiple choice answers via speech to your questions, and ask students to write just option a, b or c on the space for question 1 or 2 or whatever number it is for on their answer sheet - at least this would get them writing something that would be more within their current capabilities (if you want to insist on some form of written response to a question, rather than just a show of hands). Then, the student who writes the most correct answers (correct not just in terms of right choice but also letter shape) could win a little something (I used to have a stamp of a cute rabbit or frog - something for the girls and boys respectively!). You could even work through the rest of the alphabet a bit by having answers d through f the next week (slightly unnatural though that might be in authentic spoken "quiz English"). (Don't forget though that letters names and order are only useful for spelling and dictionary navigation, and bear less relation to the actual sounds that letters/phonemes have when connected into words and then continuous speech - some form of phonics, in other words, as Mdream mentions).
I personally always like to try to move away from possibly only
suggested syllabuses and develop and use my own methods and materials (which aren't at all bad compared to some of the dodgy stuff that's sometimes pressed onto us English teachers, often by people who don't even speak the language!), but if you're working in a hogwon rather than an actual elementary school then this may not be a real optiion.
Anyway, here are some threads that might prove interesting ('cos they detail my own elementary-school syllabus, some activities in general, and an approach to the alphabet that I developed specifically for Japanese learners i.e. which used their pre-existing literacy in Japanese kana...but I don't know much about Hangul, so can't say if something similar could be developed for Korea!):
http://forums.eslcafe.com/teacher/viewt ... 0542#40542
