Writing and speaking
I think writing and speaking have an invisible connection .Many teachers of English who teach English as a second language complain that their students make mistakes in grammar, in spite of vigorous teaching and heavy practice.One reason for this situation could be ,teaching grammar without providing a considerable background or context for the learner.This is what many experts and scholars believe.
However speaking skill of the learner is also responsible for this weakness.When learners are trained to speak through vigorous activities they learn grammar better.
Therefore it is always effective and productive to mixed writing with speaking.