When, What, Why, and How to teach is the main task of:

The correct answer is Education psychology. Educational psychology is the branch of psychology concerned with the scientific study of human learning. It provides insights into *when* students are developmentally ready for certain concepts, *what* content is appropriate, *why* certain teaching methods are effective, and *how* to optimize the learning process. It directly informs pedagogical decisions.

• Educational philosophy deals with the fundamental aims, values, and purposes of education, rather than the practicalities of teaching and learning.
• Economics and History are broader fields that provide context but do not directly address the 'when, what, why, and how to teach' in a pedagogical sense.