Yes.
A pupil or student is considered to be any person aged at least 15 years and not having reached the age of 28 years, who is enrolled in an educational institution, whether in Luxembourg or abroad, and who regularly follows a full-time course of study.
Thus, from the moment a student is regularly enrolled in a foreign institution whose school holidays differ from those in the Grand Duchy of Luxembourg, they may be employed under a student contract.
A school attendance certificate can serve as proof that the student is on holiday.