The physics that underpins modern technology is based on Einstein's theories of relativity and quantum mechanics. Most school students complete their compulsory science education without being taught any of these Einsteinian concepts. Only those who take a specialised physics course have the opportunity to learn modern physics. In 2011, the first study of a modern physics teaching intervention with an Australian upper primary (aged 10-11) class was conducted. The initial intervention was the first step of the Einstein-First collaboration towards challenging the current paradigm of Newtonian teaching in schools. It was found that modern physics concepts could be taught to these students. In 2020, 11 participants of the initial study (out of a total of 26) were contacted for a follow-up questionnaire and interview to investigate any long-term impact. The results of the follow-up indicate that the intervention maintained a positive impression on participants. The models and analogies used during the six week intervention were highly memorable. The participants indicated that they found the intervention to be beneficial to their future learning. Even close to 10 years after the intervention, the participants remembered several key concepts (such as curved space-time). The long-term follow-up indicates that Einsteinian physics can be taught at the upper primary level and be recalled several years later.