These days more than writing, speaking and understanding the subject is more important. Communication skills are very important. In earlier days many students are not able to get up and talk about what they know because of fear and shyness. But they are able to write on paper very nicely. This may be good for writing the examination and passing the test. But these days how to present yourself before the people is more important. You should have more communication skills and spontaneity is a key factor. For that speaking and communicating is more important. Asking a 1st class student or 2nd class student to read and speak is better. But once they come to 5th or 6th class the schools may be giving importance to writing.
I feel speaking will improve the kids' vocabulary and talking skills will improve. These days we see small kids talking, dancing, singing on TV channels. This will give them more self-confidence and they will grow fast in their life. If we insist on writing they may not be able to concentrate on vocabulary and their time will go in practising writing,