Planning a successful integrated STEM lesson to solve problems is not an easy task for one teacher. The involvement of multiple disciplines in the problem-solving process suggests that working in teaching teams comprised of teachers with different expert knowledge would be more productive. Each teacher brings along their expert disciplinary knowledge and skills to plan meaningful activities and select appropriate strategies to guide students to learn, select, retrieve, and apply relevant disciplinary knowledge to make connections between the problem and solutions generated. The vignette described in this chapter describes how Ms Fanny and her colleagues worked as an interdisciplinary team, with each member contributing their individual areas of expertise, to create rich and transdisciplinary learning experiences for their students. The team planned a series of lessons by weaving specific subject-matter knowledge and disciplinary skills into a problem-centric lesson on wastewater treatment. In the planning stage, the team ensured that the problem presented must be a problem related to the real world, offering students opportunities to work together so that they could practice the valued 21st-century competency of communication and collaboration. The targeted specific learning outcomes that the team of teachers included in their lesson plan were: (1) recognise the steps involved in problem solving, (2) perform water quality test, and (3) gather information and evaluate wastewater treatment. As described in Figure 6.1, the issue is presented to the students in the form of wastewater polluting the school environment and left untreated before disposal. The learning outcomes for science come from various topics and include concepts of turbidity, light, filtration, flowrate, and properties of materials. For mathematics, the learning outcomes are less extensive (hence the thinner lines of the box), with students learning the relationship between time and distance in the measurement of flowrate, learning the various formulas for geometry, and appreciating the role of mathematical and computational thinking in coding. For engineering learning outcomes, the teaching team had two intentions for students to (1) experience designing a water flow and filtration system and (2) convert their design into a physical working prototype. Lastly, students were taught how to use the technological tool Blendy (https://Blendydomevj.com" xmlns:xlink="https://www.w3.org/1999/xlink">Blendydomevj.com) to generate a 3D model and also how to do block coding using Micro:bit (https://microbit.org" xmlns:xlink="https://www.w3.org/1999/xlink">microbit.org) to operate the turbidity sensor. The connection between science-technology and engineering-technology is stronger than that between mathematics-engineering and science-engineering for this activity. As the development of 21st-century competencies is highly valued in the school, the team also intentionally created spaces for students to practice collaborative and communication competency through this activity. The plan guided the team in their decision regarding expert responsibility, teaching strategies, time allocation, and resource acquisition.