Teaching is a separate competence and it is assumed

A skilled practitioner is not automatically able to explain.

Recruitment in this sector selects primarily for vocational expertise, which is correct and insufficient. The additional competence required is the ability to make something learnable by somebody who does not yet know it, and expertise actively works against it, because the expert has forgotten what not knowing was like.

The specific difficulty is that an expert performs the task as a single fluent action and cannot readily decompose it. Asked to teach it, they demonstrate and expect imitation, which works for some learners and leaves the rest without any account of what they are supposed to be doing.

What helps is knowledge of where learners characteristically fail at each point, which is a distinct body of knowledge that accumulates through teaching rather than through practising. It is also transferable between trainers, which is the strongest argument for structured time within a department.

New trainers should be paired rather than briefed, and the pairing should run long enough to cover a full delivery cycle. A trainer who has watched somebody experienced handle the topic that always goes wrong has learned something no induction conveys.

The teaching qualification provides a foundation and is not this. Nothing in a general teaching credential tells somebody which part of a particular trade task learners consistently get wrong, and that is the knowledge that determines whether the teaching works.