The National Science Foundation GK–12 program has made more than 300 awards to universities, supported thousands of graduate student trainees, and impacted thousands of K–12 students and teachers. The goals of the current study were to determine the number of sustained GK–12 programs that follow the original GK–12 structure of placing graduate students into classrooms and to propose models for universities with current funding or universities interested in starting a program. Results from surveys, literature reviews, and Internet searches of programs funded between 1999 and 2008 indicated that 19 of 188 funded sites had sustained in-classroom programs. Three distinct models emerged from an analysis of these programs: a full-stipend model, in which graduate fellows worked with partner teachers in a K–12 classroom for 2 d/wk; a supplemental stipend model in which fellows worked with teachers for 1 d/wk; and a service-learning model, in which in-classroom activity was integrated into university academic coursework. Based on these results, potential models for sustainability and replication are suggested, including establishment of formal collaborations between sustained GK–12 programs and universities interested in starting in-classroom programs; development of a new Teaching Experience for Fellows program; and integration of supplemental fellow stipends into grant broader-impact sections.