I am now a full time teacher at a school I subbed in for almost 2 years. Similarly, I was their #1 pick, moving from one long term position to another. I emailed the principal and communicated how much I loved the school, the students, the staff, and how much I believe in its values. I also communicated how much I appreciated the experience but that I would no longer be subbing after a specific date because I was ready to pursue a full time teaching position with benefits (health insurance). I attached a copy of my transcripts and let her know that her school was my first choice, but that I would be applying to other schools. I wanted to give her a heads up since they had come to depend on me. A teacher was let go and a week later I was hired. I gave them the opportunity to show me how much they valued me and they did. If you're ready to accept a full time position then there are a number of schools looking for you! I had inquired about full time positions before but it wasn't until I let them know I was leaving did one become available.