STEM presents a challenge to education at large. The enrollment numbers in higher education STEM tracks are ever-decreasing numbers all around the globe. More so, young people's interest in and attitudes towards STEM seem to be free falling. Educational interventions that can help boost the attractiveness of STEM are therefore needed, and diverse such interventions are implemented worldwide. We present a longitudinal impact study of a STEM education intervention focusing on the attitudes of pupils towards technology. The intervention involves young students visiting a high-tech truck (Techno Trailer) at their schools. Inside this truck grade 5 and 6 students (average age 11 years) experience diverse interactions with high tech material and exhibits, focusing on how technology can contribute to solving problems in industry and society. 1496 elementary school students aged 10-12 years old (grades 5 and 6) participated in the study. Some of their teachers were prepared for the visit through a preparatory workshop, while others were not. We used the PATT to measure the pupil's attitudes towards technology. Three separate measurement occasions were included: just before, 3 days after and 3 weeks after the intervention. Differences between the measurement occasions reflect changes in attitudes over time. Overall, the study shows that the intervention rendered technology as less boring, more interesting and more viable as a career option for the pupils. For girls specifically, the intervention contributed to reversing the gender stereotypical view that technology is mainly a topic for boys. For boys we did not observer such an effect. The immediate educational impacts (3 days later) tended to decrease across time but most remained significant (3 weeks later) as compared to the base line. The results of this study show that short-term high-tech STEM education interventions can positively impact on students' attitudes towards technology. At the same time, they show that such interventions in themselves are not enough and that they need to be part of a wider strategy to boost STEM attractiveness. Furthermore, our results highlight the added value of the preparatory workshop for teachers in terms of generating educational impact on pupils' attitudes towards technology.