Although I’m an ALNCo (SENDCo) in Wales, our systems are similar. It’s a difficult position when you take over as a new Senco as you might not know the history of parental and student involvement of a child being identified with SEND and if the correct and / or advised protocols were followed. There should be parental partnership from the very start.
Take a look at the NASEN guide ( Google search: NASEN SEND Guide 0- 25 years) p7 Chapter 6 ‘Schools ‘ Action panel in blue.
Hope this helps . . . and best wishes in your new and rewarding post!