Several entities provide free webinars of interest to school librarians. Here is a sampling:

http://www.webjunction.org/find-training/free-events.html

http://www.slj.com/category/webcasts/

http://lj.libraryjournal.com/category/webcasts/

http://education.sla.org

http://www.ala.org/onlinelearning/schoollibraries (see are fee-based)

https://www.tsl.texas.gov/ld/workshops/webinars/index.html

http://www.follettsoftware.com/webinars.cfm

http://ideas.demco.com/category/webinars/

https://oclc.org/events/webinars.en.html