Speaking by its very nature is ephemeral. As a teacher, it's the skill that I find most difficult to correct. Do I interrupt and impact on fluency? Or should I wait until the end and board some of the most common errors? Either way, I seem to correct the same errors again and again. The students can often identify the mistakes they've made relatively easily but they continue to produce the errors. Those are just the grammar and vocabulary issues. What about the task itself? In a group of 12 students, when perhaps 6 people are completing the task simultaneously, I can't tune in to them all at the same time. I often ask the partner to evaluate, but 99% of the time they lack the confidence to say anything other then it was 'good'.
Are you a teacher looking for opportunities to continue your professional development? Why not join an elt book club? Jenni Fogg writes about it here.