I've been having lots of success with the mastery model, and the best part has been that it makes my teaching time (and my students' days) less stressful and (I believe) more productive and effective.
But I've been struggling with whether it really does just take too much time. if you allow studentsto revise and resubmit everything, that multiplies the time requireed for grading. And if you need ot redesign assignments to fit the mastery model, that multiplies planning time.
And while there may be some teachers who go home every day at 2:30 and don't work weekends, I don't know them. In other words, they don't have a lot of extra time during the school year to spare. And as I've mentioned before, U.S. teachers already work half-again as many hours as the OECD average.
But here's what I'm thinking:
1) I don't do mastery because it is convenient, but because I believe it works for more students.
2) I'm not convinced it will mean extra time in the long run. After the initial redesign phase, the extra planning time will be a non-issue. And I think the extra grading time can be partially balanced by, a) automation and, b) replacing some formal scoring with informal teacher feedback and/or peer- and self-assessment.
I believe that quantitative, objective-as-possible scoring (i.e. data) is essential to real instructional improvement, but not every activity needs to be scored in this way, and some could be automated (as I currently do with short content quizzes).
This is exactly what I've been working towards lately with my new system: employing more informal feedback before the students submit an assignment, and using student self-assessment as a supplement to my own assessment of their work.
Though a switch to the mastery model will take more time up front, I think it might not require more than the traditional model after it's fully implemented.
The trick is, how do you create this massive paradigm shift and support this large initial spike in input to get the change to take place?