The Librarian in 'the whole scheme of things'

How does the TL fit within the school?
We read that the TL is the Principal's representative and is the one to make decisions regarding acquisition and collection on behalf of such.How does this actually fit into everyday practice? How is the Collection Management Policy (CMP) followed within schools?
Within the school that I am the TL, the CMP is new. The principles of the CMP are one's that I believed were currently being followed within this school. I was to find out that they were not. Resources are being orderd by executive on staff and sent to the library for accessioning, without knowledge by the TL. Where do these resources fit into the curriculum? Are they the best resource for this purpose? Could we have bought cheaper, more alligned to the curriculum? Could the TL, with her contacts, received a better deal on this purchase?
In this situation, the TL will need to sit with all executive and axplain the CMP and processes involved with selection and acquisition. The challenge will be to do this without coming across as domineering or dictatorial.
I believe that the TL should be the acquirer of resources due to access to publishers and, sales companies and the knowledge base of how to follow orders through.The TL has an overall view of the collection and knows the direction the school is taking.
The CMP is a changing, working document that is a policy to be followed by all staff. The job of the TL is to produce this document, with executive support, to staff and ensure that the policy is followed. A difficult job if you are in a large school.