Self and peer assessment is very fashionable and has been for a while. Ofsted seem to like it, teachers seem to like it and SLTs seem to like it too. Having used a variety of types of methods of peer and self assessment in my teaching career, I am yet to be convinced of the impact they have.
As teachers look for ways to cope under the crushing weight of complicated marking and assessment policies, peer and self assessment can offer a helping hand. If the children mark the work then the teacher doesn't have to. Crazily, I know teachers who mark it themselves as well. Why would you do that, defeats the object surely. This brings me onto the first problem with self/peer assessment. Teachers, who are under massive pressure to prove they are doing a good job, are scared to leave any piece unmarked by them. This means that the marking by the pupil during peer/self assessment becomes largely irrelevant.
Secondly, there is the issue of time. Time has to be taken from lessons to complete self/peer assessment tasks. With the raised demands that come with the new curriculum, there is simply no time to waste. Ten minutes taken from a lesson to self/peer assess could be ten minutes used to further master the learning objective of the lesson.
Teachers have spent a lot of time training to be a teacher, they are professionals with a sound understanding of the subjects they teach. They are best placed to make decisions about whether a child has achieved a learning objective and what the next steps should be. I would argue that a pupil is not capable of making these decisions effectively or efficiently. A pupil can tell you whether they have found a particular activity easy or difficult. Does this matter? Does it tell you anything about their achievement? If you are teaching a child something they have not come across before, how can they decide whether they have learned it? Surely, this is judgement that must be made by a well-trained professional. Children can find evidence in their work to show they have met certain 'success criteria' but they cannot decide whether this means that they have achieved the objective.
Peer/self assessment forms part of a larger issue around pupil voice. I am not a fan of pupil voice even though it seems to be fashionable. In terms of assessment, that should be done by the teacher as the professional or if you really want to involve pupils as a discussion between pupil and teacher with the teacher explaining to the pupil what their performance in an activity means with regard to their achievement/progress.