As of 2017 prep will be compulsory for all Queenslanders, Premier Annastacia Palaszczuk announced on Sunday.
The Premier said she would guarantee to make prep compulsory to make more children in Queensland attend.
"Prep is already part of the national curriculum and now we will take the next step and make prep compulsory," Premier Palaszczuk said.
"It's been 10 years since prep was introduced and now we have around 98 per cent of children attending.
"We know how important that early year of learning is and I don't want to see children disadvantaged by starting that extra year later, let's give all our children an equal and fair start."
Education Minister Kate Jones said her department's statistics had shown that prep is an advantage to children.
"We know that it makes a difference to children's educational outcomes," Ms Jones said.
"We know that this year is valuable."
Deputy Opposition Leader John-Paul Langbroek said the announcement doesn't allow flexibility for children who might be the right age, but developmentally they may not be ready.
"We need to also have the individual flexibility to allow parent, if their children are not ready or if principles and teachers think that the children are not ready, to not necessarily go into the prep year when the age actually arrives," Mr Langbroek said.
Ms Jones said that her department had shown the move to make prep compulsory would make attendance rise by 1.5 per cent.
"It's no longer good enough, in our view, to not say that 100 per cent of students deserve to right to go to prep," Ms Jones said.