It was always planned that they should leave to move on to the next stage of their careers, and all three have gone on to deputy headships. I have no doubt that in a few years they will all start thinking about headships.
It is still hard to let go. Our leadership team works with as few hierarchical divisions as possible. Assistant heads could be deputy heads in any other school. It is, therefore, sad that they have to go through a deputy headship in another school before they can be taken seriously as potential heads.
While it is good to gain experience in another school, it is more difficult for people at the more mature end of the spectrum to be promoted. Governing bodies are not yet open to considering colleagues who do not follow the traditional route to headship. In view of current hysteria about future shortage of candidates for the top job, this seems short-sighted.
Succession planning has always been part of our school culture. We are a large extended school where distributed leadership is all. We knew that members of our team would move on sooner or later - this is a sign of our success - and have had to plan to ensure that we could fill the posts when that happened.
So we included the posts of associate assistant headssenior leaders in our structure. These are training opportunities that are open to all senior middle leaders, including support staff. They join the senior team in as many activities as they can manage, as well as fulfilling their own role as middle leaders.
They quickly become aware of the big picture and see things from a whole-school perspective. They also form an effective bridge between senior and middle leadership.
When we advertised to fill the posts vacated by our three colleagues, we had an excellent response and interviewed a large number of candidates. We put them through the mill and tested every aspect of their professionalism.
But in the end we chose colleagues from our own school.
It quickly became clear that those who had been associate senior leaders were able to demonstrate their knowledge of whole-school issues. Even though I have worked with these colleagues for many years, I was still astounded by their performance during the interviews.
This year we had 10 applications from middle leaders who wanted to join the senior team. We were only able to take three, although we will involve the others where we can. I know I am a lucky head, but we have also engineered that luck.
Kenny Frederick is head at George Green's community school in Tower Hamlets, east London