In the following article posted by Michael B. Horn on EdSurge (May 20, 2015) we are beyond this question. It's not whether or not Blended Learning works that is the issue, but how it is initiated. To learn more check out Moving Beyond the "Does Learning Work?" Question.
As a teacher specialist working with instructional technology since 2008 I have had the "pleasure" of delivering technology based professional development to teachers in a variety of settings. Most of the time it's in person. And much of that time is spent watching disinterested and distracted professionals struggling to stay interested and engaged.
Too many teachers are maxed out!
Not only are they tired, overworked, underpaid and under appreciated, but we remove them from their teaching environments to provide professional development. This often means spending money on sub, spending time making sub plans, or worse - staying late after school. Gross.
The irony is that when providing instructional technology based PD we should use those tools to adjust the PD much like we are asking teachers to adjust their teaching. Let's lead by example. Let's "BLEND" the PD!
George Couros shares some of his insights on how to blend professional development for teachers on his blog "The Principal of Change"