Set up a 'retrospective mailbox' at the beginning of the iteration. Whenever something significant happens or someone has an idea for improvement, they write it down and 'post' it. (Alternatively the 'mailbox' can be a visible place. This can spark discussion during the iteration.) Go through the notes and discuss them. A mailbox is great for long iterations and forgetful teams.
As developer, product owner, scrum master and agile coach, Timon has been a Retromat user and fan for more than three years. He had quite a few feature ideas. In 2016 he started to build some of those features himself. You can email him or
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