A drop in school attendance due to COVID-19 is of "great concern" and shows that some children are not receiving any education at all, the commissioner for children has said.

The office of Commissioner Pauline Miceli had warned that education should remain compulsory for all but vulnerable pupils when schools reopened last month after an unprecedented seven-month shutdown.

School attendance is at 75 per cent, down from a regular 90 per cent this year after parents were given the option not to send their children to school due to COVID-19.  

Half of the missing students were not attending school because they are classified as vulnerable but the other half are cases of absenteeism, Education Minister Owen Bonnici said.

The education commissioner's office said it had already been a challenge to reach children not attending compulsory schooling before the pandemic.

COVID-19 had created even more challenges, especially since attendance is no longer obligatory, and a number of children are "falling through the gaps," it warned. 

It said that many health protocols have been put in place in schools, therefore, parents or carers should "prioritise school attendance" over other activities such as going to supermarkets.

The office stressed the need for long-term investment in remote learning for students who are not able to attend school. Students should be able to connect with their classroom live so as to engage as much as possible, it said.

Together with the Council for Children, it called on all the relevant authorities to ensure that all children are guaranteed "their right to education".