I did three to four days a week from May to July, and then one, sometimes two days a week between September and December. I had previously taught in the school for twelve years (although that was five years before I went back for the ethnography). Therefore I had worked with most of the staff, but had never taught any of the kids. Some of the sixth formers remembered me, but I hadn't taught them. There were many ethical dilemmas that occured - I have submitted an abstract to BERA to present on them this summer, but I feel that I was able to collect enough data in that time period to inform the next stage of the PhD. I managed to generate two large journals worth of data, and conduct nine interviews. In terms of making the familiar strange, and the strange familiar, I was always thinking and analysing while I was in the school - in fact I still am now as I try to finish off my methodology chapter (23000 words and two sections to go). I have a full time lecturing post, so it was/is difficult balancing the roles. I already was fully aware of the socio cultural / historical identity of the area / school / management / teachers, so there was less to do in that aspect.

Hammersley and Atkinson is excellent, but much of my material has come from the journal Ethnography and Education.

I am doing exactly the same Lixatron as I went back to conduct an ethnography in a school I used to teach in. As mine is narrative, reflexivity run right through it. I have used a reflexive diary and illustrated the methodology with critical incidents and other extracts from the diary. I have a whole section outlining my previous role and relationship with the participants. Not sure whether it will go in at the beginning of the methodology, or in a different part at the end.

I spent two terms in a school ranging between one and four days a week depending upon other commitments. This was easily enough to collect the data for my PhD - you start to get a lot of repitition after a while. In terms of books, the following are all essential.

Hammersley & Atkinson (2007) Doing Ethnography: Principles and Practice.
Delamont (2002) Fieldwork in Educational Settings.
Wolcott (2005) The Art of Fieldwork
Wolcott (2008) Ethnography: a way of seeing.

The journal Ethnography and Education is also essential for many relevant papers on methods.

Best of luck.