Education department figures show that in 2019 more than 7,500 primary and secondary students from schools in the North recorded an unexplained - unauthorised absence.

This year those numbers have increased, with more than 6,000 students recording absences in Terms 2 and 3 alone.

The government says that legitimate reasons for school absence include sickness, medical and other appointments, a family death or terminal illness.

Reasons for absence that result in an unexplained - unauthorised record may include truancy, family holidays, keeping the child at home, or simply, that the parent has failed to notify the school to provide any explanation.

Tasso president Jared Dickason said communication between parents and schools on this issue was an area needing improvement.

"There are many factors that lead to absence but fundamentally there is probably a breakdown of communication between schools and parents to understand where the child might be and what they might be doing," he said.

"One of the things we are really working on is engagement, and also communication between schools and parents. Parents need to understand that we have an obligation in this."

Of the 2020 absences, he said disengagement may be one cause but it is a complex matter with many variables.

He said living in homes with family whose health conditions increased the risk of Covid-19 was, and still is, a common reason for absence.

"The more understanding we can obtain through conversation with family the better chance we have of lowering these figures and place children in the best position to succeed "

Tasmanian Principals Association president Sally Milbourne said school disruption resulting from the Covid-19 pandemic was still having an impact.

"What I don't think we know yet is what impact Covid-19 has had. Clearly students were working remotely from home and then, when schools reopened again, what happened to some of those students?

Australian Education Union Tasmanian president Helen Richardson said it had been a disruptive year for many students and called for extra support in schools.

"Teachers, principals and support staff had to change everything almost overnight in response to COVID-19, including how we deal with student absences. Now teachers, principals and support staff face the difficult task of trying to re-engage students who may have struggled with attendance even before COVID-19 disrupted everything," she said.

"What we really need is additional staff and resources to engage and support students and work with families to tackle the barriers students face - barriers that prevent them attending, or make focusing on learning impossible."

The education department said a school will contact a parent or guardian on the day of absence to request a reason, and until a reason is obtained that absence will be recorded as unauthorised - unexplained.

Schools continue to follow up with parents.