This is my experience in Worcestershire:
LA decided to "consult" with schools and parents re. going from 3 tier to 2 tier for a number of reasons. I believe they are as following (although we never really got a clear answer).
Every initiative/curriculum/support package from the government is aimed at the 2 tier system. LAs which run a 3 tier system, therefore, spend more and work harder to support a 3 tier system (which costs more money).
There is the expense of having an entire extra layer of schools which cost a great deal to run.
The educational/emotional benefit of 3 tier is unproven, compared with the financial benefit of 2 tier.
Children's attainment suffers each time there is a major transition, so the fewer transitions, the better.
Falling roles meant that there were spaces in most schools, and the review meant that certain schools would close, making the LA more cost effective.
First, a list of the closing schools was published.
Then, they nominally closed ALL the schools on 31st August 2007 and re-opened as Primary and Secondary Schools on 1st September. Effectively, they closed all middle schools, but rather than simply require the middle school staff to apply for new jobs, it was felt fairer for ALL staff to have to re-apply.
First, temporary governing bodies were created from combined first and middle school governing bodiess. They then started by appointing all the Headteachers, then Deputy's etc. All secretaries, caretakers, teachers, TAs, lunchtime supervisers etc. had to be interviewed. Strict guidelines were in place to ring-fence jobs in the affected region to ensure that as many people as possible were re-deployed.
In terms of the children - in 2006, First schools kept their Year 5s, which meant that by September 2007, those Year 5s were Year 6s, giving a full primary school.
Those children in the middle school stayed there, but the number of year groups in the middle schools got smaller until the final two year groups (7 & 8) moved across to the secondary schools together.
In the intervening years, a major building project started to extend/remodel/update suitable schools. In the meantime, children were educated in temporary classrooms, generally on the Primary and Secondary sites.
In spite of all of the above, I still feel that going to 2 tier was the right thing to do.
My fingers are tired now! If anyone has read the above and wants to ask any questions or comment, I'll be back later.