For example, teachers started evaluating each other through informal observations, they introduced team teaching, coaching and mentoring programmes, and also visited other schools to see how they worked. (tdtrust.org)
In my own first two years of teaching, I was evaluated each year with both formal and informal observations by my administrator. (articles.latimes.com)
To ease any anxiety about informal observations (particularly if this is a new practice) I recommend that an observer begin by announcing the day or the week these will be taking place. (marzanoevaluation.com)