There is a new Best Evidence in Brief with – amongst others – this report:
A new report from the Institute of Education Sciences has found that an intensive approach to helping principals improve their leadership practices did not improve student achievement or change principal practices as intended.The study looked at the effectiveness of a professional development (PD) program for elementary school principals that focused on helping them to conduct structured observations of teachers’ classroom teaching and provide targeted feedback. It provided nearly 200 hours of PD over two years, half of it through individualized coaching. One hundred schools from eight districts in five states took part in the study. Within each district, schools with similar characteristics were paired together, and within each pair, one school was randomly assigned to participate in the program for two years while the other did not.To measure the effects on student achievement, the researchers compared student test scores in grades 3 to 5 for both years of program implementation plus one additional school year. They found that, on average, students had similar achievement in English or math whether they were in schools that received the principal PD program or not.The results of the study also found that although the program was implemented as planned, principals did not increase the number of times they observed teachers. In fact, teachers whose principals received the PD reported receiving less frequent teaching support and feedback than teachers whose principals did not receive the PD.
From experience to meaning... 
Hi Pedro, I’d like to note that buried in the report is this: “The program encouraged principals to conduct frequent classroom observations and document what teachers and students did and said in the classroom using a nonjudgmental, fact-based approach. An instructional framework and observation rubric guided principals’ observations and documentation.” Endnote iv led to the Danielson Framework as that rubric. Just as with the Gate’s Foundation/RAND study where the Danielson Framework was used in all but one of the school districts, the fatal flaw is constructivism, which the DF is based on–in the book that goes with the Framework, Danielson makes no equivocation that her system is built on constructivist theory and student engagement is at its core. Until that fundamental flaw is addressed, then these studies are doomed to show what they do.