The census of ACT schools conducted in February 2022 shows the rate of enrolment growth slowed considerably in 2021.

The new figures show primary enrolments increased by 85 students, high schools increased by 585 students and colleges increased by 121 students.

But preschool enrolments dropped by 490 students between 2021 and 2022, which represents an 8 per cent decrease.

The ACT government has put this down partially to a drop in the estimated number of three-year-old children in the ACT, which was 300 less than the estimated amount in June 2020.

The government also suggested some parents were choosing not to enrol their children in non-compulsory preschool education because of a rise in cases in early 2022 and the fact that children under five cannot be vaccinated against COVID-19.

University of Canberra Associate Professor in early childhood and communities Deborah Pino-Pasternak said systemic issues due to lack of universal access to preschool services and the financial burden on families could also be a factor.

"I believe that another unspoken issue has to do with how women have been affected during the pandemic, in terms of workforce access, and opportunities for care for their children," Dr Pino-Pasternak said.

Dr Pino-Pasternak said it was concerning from an education perspective if parents were not sending their children to preschool.

The latest Australian Early Developmental Census showed between 2018 and 2021 a decrease in the percentage of children who were on track to reach five developmental domains and an increase in the number of children who were vulnerable in one or more areas.

"There is a strong economic argument ... every penny that's invested in early childhood education prevents reactive expenditure later on in terms of mental health, physical health ... recruitment at the level of workforce, reduction in criminal offences," Dr Pino-Pasternak said.

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The school census figures showed the number of preschoolers enrolled in public schools dropped by 8.9 per cent while the number enrolled in independent schools dropped by 10.1 per cent.

Catholic school preschool enrolments across eight centres held steady with 1.6 per cent growth, the equivalent of 10 extra students.

Preschoolers at St Thomas Aquinas Early Learning Centre moved into a brand new building last week.

Principal Leah Taylor said it was vitally important for children to have access to preschool.

"They may not go to playgroup so they learn how to take turns and learn how to share," Mrs Taylor said.

The educators guide the children through loose-parts play, telling stories and expanding their vocabulary.

The new facility even has a kitchen and dining room for children to learn how to cook a dish and share it together.

"They'll sit down and share a meal and we talk them about ... how do you behave at a table? How do you share a meal? ... they that sort of learn those skills as well," Mrs Taylor said.