I have observed multiple online references to teaching for mastery in the last couple of months. I have mixed reactions based on a career-long interest in mastery learning. On the positive side, seeing new interest in an old idea that I believe is typically novel to most educators is encouraging. On the other hand, it seems present interest involves a narrow perspective on what teaching for mastery originally meant. Teaching for mastery is more than allowing students a second chance to demonstrate their level of understanding or competence.
I think the original teaching for mastery approaches offer great possibility now that technology can offer ways to implement the components of mastery instruction as originally proposed. I think mastery faded not because there were not benefits to students, but because the demands of implementation were too great. To me, mastery based models were a way to respond to the differences in time to learn required by different students. These differences could be a consequence of differences in aptitude or in the success of past learning experiences. A successful approach combined multiple components and not simply the willingness to provide students a second chance. While an important component, nonpunitive, second chances still assumed all students will move on at approximately the same rate.
I have made an effort to describe what I understand to be a be a more complete approach to mastery based instruction previously and if interested, I refer you to these comments- https://learningaloud.com/grabe6/Chapter4/ch4_mastery.html