The CERN International Masterclass is an international schools engagement programme that takes place over several weeks each spring and reaches more than 10,000 young people from more than 60 countries. Lancaster University is one of 200 institutions from around the world that participates in the programme by hosting one or more masterclass events. Each event lasts a full day and consists of outreach talks about cutting-edge topics in particle physics, a hands-on practical session where students have the opportunity to perform computer-based measurements using real data from CERN, and a final online video conference hosted by a CERN research scientist. In February 2020, the Lancaster Particle Physics group participated in a special CERN masterclass, celebrating the International Day of Women and Girls in Science. The event was attended by a group of Y11 students from Lancaster Girls Grammar School. The delivery was supported by a team of research staff and student ambassadors from the Lancaster Physics Department.