While some students and parents were happy to be back in school, others were worried about the coronavirus.
In Germany, only eight states returned to school on Monday as the country reported three times the number of COVID-19 infections within 24 hours from a week earlier.
Sixth grade student Lucia said it was nice to back at school with her friends.
The school tests their students and staff three times a week and obey hygiene rules, according to Lucia's teacher.
Portuguese students headed back to school a week later than usual after authorities postponed the start date in order to tackle a surge in COVID cases.
According to local media in Italy, about one in three classes will be empty, with students forced to attend lessons at home.
The country's current coronavirus rules impose that if there is one positive case in a secondary school class, the remaining students will continue to go to school wearing FFP2 masks in the classroom and showing proof of a fresh negative test.