Under the law, children who turn six in the year in which a school year starts must be enrolled in first grade.
But if parents believe their child is not ready or mature enough to start school, they have the right to request a deferral; such a request can also be made by a doctor.
Schools decide on these motions and they rarely go against parents' wishes, the head of the Association of Slovenian Parents Councils, Anton Meden, told the STA.
The decision is made based on an evaluation of the child's intellectual, physical, emotional and social skills.
In the last seven years, the number of delayed enrolments almost doubled, according to data by the Education Ministry.
In 2010/2011, 4.5% of pupils started school with a one-year delay; in 2014/2015 their share rose to 6% and in 2016/17 it was as high as 8.3%.
According to the ministry, parents request the delay to give children one more year of carefree childhood or because they fear the child will not be up to school tasks yet.
Meden said that he had talked to many parents who regret not opting for a deferral but virtually none who would regret delaying the enrolment.
Parents can also send their child to school earlier than legally required but very few of them do.