What is it?
Generally speaking, it's a focus on the development and growth of individuals and organisations (me and my school in this case).
More specifically, it refers to a wide variety of specialised training, formal education, or advanced professional learning intended to help educators improve their professional knowledge, competence, skill, and effectiveness.
Sometimes this involves a meeting after school on a Monday afternoon in a hot and stuffy staff room.
What is it good for?
If it is true to its intentions it can be great.
But if the professional development is poorly designed, executed, scheduled, or facilitated, or if teachers feel that it is irrelevant to their teaching needs and day-to-day professional responsibilities, then at best it's seen as a waste of time, at worst it can have a negative, destabilising impact.
When is the optimum time for it?
According to Stanford University it needs to be embedded in substantial planning and collaboration time at school.
I think the key words is EMBEDDED - to be an integral part of a surrounding whole.
Why is that many many schools feel that after school on a Monday is the right time to schedule something that should be an integral part of a teacher's professional development?
The best example I've experienced was at Woodford House a few years ago when staff embarked on an inquiry project of their own design. Ultimately these projects, which lasted for a number of school terms, resulted in meaningful change to individuals AND the organisation.