The main goal of this study was to improve students’ outcomes and perception in Mathematics. For this, 12 out of 34 voluntary students were involved in an international contest: European Space Agency (ESA) Mission Space Lab. The experience was organized as STEM, under a guided PjBL. Students identified an environmental problem, executed a way to monitor it from the International Space Station (ISS) and interpreted the data received. Students’ final report was awarded by ESA. Additionally, participants increased their performance in their math final exams compared to the control group. Furthermore, the perception of students and their families about the usefulness of mathematics was very positive. The only drawback detected was the increase of workload. Thus, Green STEM, using direct instruction and guide in PjBL, may be a good tool to improve students’ grades and opinion about the importance of mathematics.