Background: Previous research into children's perceptions of science shows that children like science but often hold stereotypical views of scientists and commonly do not see themselves with a career as a scientist. Purpose: The aim of this study is to examine if a carefully designed medium-term, teacher-led STEM intervention, 'Scientist of the Week' which showcased a diverse range of working scientists and the skills they need, can lead to a positive change in the perception of scientists among young people. Sample Design and Methods: Using a case-control approach, this research used a tracked sample of 118 young people from aged 7 to 11 in a primary school in the North East of England. Words associated with scientists were collected before and after (directly, one month, one year) the intervention from the tracked sample and analysed to assess changes in stereotypical perceptions and any difference in responses between male and female participants. Results: Before the intervention, young children held many of the common stereotypes associated with scientists. Shortly afterwards, and one year following the intervention, the use of common stereotypes had fallen significantly across all children, with particular improvements in counter-stereotypical word usage for males. It also found that stereotypical images of scientists as highly intelligent were more difficult to counteract and that many of the positive changes in this view seen in the short term (weeks and months) diminished in the long term (one year later). Conclusions: This research has shown that with minimal expense and effort from teachers, negative stereotypes of scientists can be reduced through an intervention that does not require bringing scientists into the classroom. Some of the observed changes persisted in the longer-term, suggesting a lasting alteration in children's perceptions of scientists following the intervention.