We offer a concise history of teacher retirement plans in the United States, highlighting the increase in the generosity of the plans over the past 25 years. We employ data from plans in all fifty states to estimate the impact of a set of social and economic variables on the plans' replacement rates for a hypothetical teacher. We find that, at the state level, population growth and the share of the labor force that is unionized positively affect replacement rates; while expanding plan membership to include other state employees and participating in Social Security negatively affect replacement rates. Two appendix tables and bibliography are included. (Contains 3 figures, 6 tables and 10 endnotes.)