Lateral flow assays play a key role in mass testing for COVID-19, for example, in schools. The red color of the detection lines is caused by gold nanoparticles that are conjugated to antibodies. Hence, these tests present a very topical learning opportunity in the emerging field of nanoscience. To highlight the role of gold nanoparticles, a low-cost model of a lateral flow test was developed and used in high school. First, peptide-conjugated gold or silver nanoparticles are synthesized. During the reaction, color changes occur that can be explained by the increasing nanoparticle size. The product solution is then used for the assembly of a model lateral flow test. All of the experiments can be performed by high school students. The modeling of this state-of-the-art analytical method can support learning in nanoscience and can provide insights into the nature of scientific models.