Previous studies have revealed that preservice science teachers (PSTs) require more robust and stimulating opportunities to engage with and reflect on formative assessment (FA) during teacher education. From a sociocultural-asset perspective, 16 PSTs participated in a co-design process with researchers, engaging in an iterative reasoning and development process of an FA-embedded chemistry laboratory learning environment through the conjecture mapping approach over the course of a semester. This case study presents how a randomly selected small group of PSTs (N = 4) implemented the co-designed FA practices for one of the most challenging chemistry topics, chemical equilibrium, in a laboratory setting in the subsequent semester. Several data collection tools, such as audio records and artifacts from the PSTs' FA enactment in their laboratory investigation, were used in this study. All triangulated data was analyzed using the method of interaction analysis to generate and interpret meanings. Findings revealed that the PSTs could implement FA by interweaving five key FA strategies to enhance their learning in the chemistry laboratory. Specifically, the findings showed that not only the content and quality of feedback but also the way feedback is used and interacted with in FA play a critical role in improving the PSTs' learning and performance. This study has implications for designing and testing FA-embedded learning environments that must be created "with," "not for," PSTs from sociocultural-asset perspectives to improve the quality of FA.