MatReLan builds on the experience gained by the two partner-schools within the Learning math and languages through research and cooperation/MatLan project. During MatLan project, a KA2 Erasmus+ project (2014-1-RO01-KA201-002699) implemented in 2014-2016, we elaborated the syllabus of the elective course "Doing math as researchers do it". MatReLan project aims to support the partner-schools to provide opportunities for the high-school students enrolled in the elective course to develop their mathematical, transversal and language skills through conducting mathematical research and online collaboration with students from an EU country; Math teachers will share experiences and improve the delivery of the elective course.