This study compared two versions of professional development (PD) designed for teachers using formative assessment (FA) in mathematics classrooms that were networked with Texas Instruments Navigator (NAV) technology. Thirty-two middle school mathematics teachers were randomly assigned to one of the two groups: FA-then-NAV group and FA-and-NAV group. The FA-then-NAV group received PD in formative student assessment in the first year and PD in using networked classroom technology for formative assessment in the second year. The FA-and-NAV group received PD in using networked technology to implement formative assessment in two consecutive years. We examined the change of teachers' self-reported knowledge of formative assessment, self-efficacy in formative assessment, and attitudes toward the use of technology, as well as their evaluations of the two PD versions, by surveying the teachers at pretest, after Year 1 training, after Year 2 training, and after Year 3 (without training). We found significant growth in knowledge about general assessment, knowledge about formative assessment, self-efficacy in formative assessment, value of technology, and confidence in classroom technology for each version. While no significant differences were found between the two versions on the measured constructs at the end, different growth trajectories were observed in each group over the three years. The majority of the teachers reported that they preferred the FA-and-NAV PD version.