This is a question for the ages, isn't it? Check out this 2010 interview of Dr. Kylene Beers and Dr. Bob Probst.
What Dr. Beers and Probst say is true. If you haven't time to watch the video (or can't just know because of where you are), let me sum up and amplify a bit.
First, effective professional development means the educator is thinking continuously about his or her profession. And as educators think about their profession, they think about what they can do differently. Dr. Beers makes mention of other professions to which we also refer as "practice." Lawyers and doctors have a practice. Most professions have on-going certification expectations or expectations that those in the profession will continue to do research, read research, participate in conferences and other opportunities to learn more to improve and increase what they know and how to apply that learning. Why? So they can do a better job for their patients or their customers. They need to be as current as possible.
When educators go to conferences, they self-select the sessions they want to attend. One of their objectives is to learn something they can use in their classrooms, schools, or buildings. They want something practical and applicable, perhaps based on theory but most certainly borne out in practice. They want to leave each session with "stuff"--lesson plans, guides, materials, links, whatever. Something usable. Immediately. Now. Something that can help them make a difference with their customers: their students.
Second, drive-by, one-day inservice events are generally of little use. I say "generally of little use" because if the events are well-planned and fit within the context of other work the district is doing, those days can make a difference. Much depends on the communication between customer and presenter, between the individual coordinating the PD and those who will participating in that event.
I've done stand-alone PD events after solid communication with the customer. I do my homework, ask the right kinds of questions of the customer, and do quality preparation and presentation, most of the folks who attend that event, much like those who attend a single session at a conference, will learn something they can use. But I also know that if my event is part of a year-long plan and each single meeting builds on prior meetings and prepares the way for subsequent events, better things might happen in classrooms, schools, or districts.
I've done stand-alone PD events after less-than-solid communication with the customer. That usually means a lot of on-the-spot adaptation by me to make sure that the participants can walk away with something other than aggravation about a lost day.
Third, effective professional development demands accountability. What happens after the event ends? Does the whole group then split up to work with its grade-level team or PLCs or department or team? Does each individual make a list of specific next steps with an understanding of why those next steps are important and with deadlines attached? And do they review their next steps with someone else as an accountability partner? In other words, how will anyone know if that professional development experience has made one iota of difference? How will the participant herself or himself be able to explain how attending and engaging in that PD event shifted any thing in his or her practice?
here. You might read more on reflective practice here.
The point is that good reflection can't come from just one vantage point. We can't see ourselves clearly, and not just because the angle is often awkward, but it's hard to be objective. But thoughtful and intentional reflection can serve to help us continue to improve what we do and how we do it.
Finally, it needs to support the teacher. I've worked with some groups who have rejected pretty much anything and everything because I wasn't meeting their needs. Sure, sometimes that can be the teachers are just being recalcitrant. But sometimes it's because the content or the application or the resources or something just doesn't fit. What works in one school might not work in another and for a whole range of reasons. So, again, the more homework I do to understand the needs of the teachers, the demographics of the school and district, and more, the better able any presenter is able to tailor the event.
At the end of the PD day, it is about making sure that educators learned something that makes a difference in how they see themselves, how they view and change or modify their practice, how they continue to reflect on themselves and their practice, and how they continue to try to improve to make sure their kids can be as successful as possible.
Effective professional development is not about the teachers. It's always, always, always, always about the kids and their learning. The better educators are at their practice, the more they know about themselves as learners and teachers, the better the learning experience will be for their students.