Coherence is one of the two qualities that give a written or spoken text unity and purpose. The other is cohesion. Coherence refers to the general sense that a text makes sense through the organisation of its content. In writing, it is provided by a clear and understood structuring of paragraphs and sentences in writing.
A learner's argument essay is coherent because it has a structure that gives unity and follows an accepted form. It begins with a statement of belief, gives the opposing arguments, refutes these, and summarises in a final paragraph.
In the classroom
Coherence in written work and extended speaking, e.g. presentations, can be practised by looking at suitable organisation of content, and by planning exercises.