An inquiry-based integrative STEM education approach was implemented in two fourth grade Elementary Education classes, in Spain, through a module on simple machines. The viability of this science education model in the official Spanish curriculum and its influence on students’ attitudes towards science and learning of STEM subjects has been studied through an adapted Test of Science Related Attitude scale, achievement tests, and teachers’ interviews. Students participating in the integrative STEM project reported significantly more favourable attitudes toward science than students from traditional classrooms. Although attitude scale and achievement test results seem to show that an integrative STEM education may be feasible in 4th grade of the Spanish elementary education, interviews revealed reluctance among teachers to use integrative STEM education and more directive instructions on implementing such an educational model are demanded. Implications for science education and future studies are discussed.