Mathematics is traditionally taught using direct instruction, which has been found to engender negative affective responses towards the subject, including anxiety and low self-efficacy (Borko et al., 1992; Mischo & Maas, 2013). Direct instruction places authority on the instructor and involves teaching students about mathematics instead of teaching them to do mathematics (Gilat & Amit, 2013; Schukajlow et al., 2019). Productive Failure (PF), in contrast, teaches students how to develop their own approach to solving problems and thus improves conceptual understanding and transfer (Kapur, 2008; Kapur & Toh, 2015; Loibl & Rummel, 2014). The purpose of this study was to expose in-service mathematics teachers to the PF problem-solving process and to examine how their self-efficacy and mathematical affect were influenced. During problem-solving, participants' self-efficacy was negatively impacted by encountering an obstacle, having no clear direction, and lacking content knowledge. Self-efficacy was improved as participants developed their own solution strategies and used the real-world context as a tool. Mathematical affect was improved as participants collaborated on a PF task and as participants felt satisfaction with their work. Later interviews corroborated these findings, also indicating that negative influences on mathematical affect included having insufficient information and difficulty in collaborating with certain peers. The positive influences on affect also included collaboration, the context, developing one's solution strategy, and having opportunities for creativity and satisfaction. Though PF has not been previously connected to self-efficacy or mathematical affect, core components of a PF problem-solving session were found to likely improve both of these for the participants. Negative aspects were generally overcome by one or more of the positives. It is recommended that PF be incorporated into mathematics classrooms intent on improving the mathematical affect of its students. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]