The First Minister's Reading Challenge was launched in 2016 in partnership with the Scottish Book Trust, aimed at developing a life-long love of books.
Originally designed for children in primary four to seven, it will now include all primary school pupils.
Nicola Sturgeon said the initiative "has been a fantastic success since it was launched".
The challenge encourages children to choose from a list of 100 books, specially selected by a panel of academics, experts and teachers.
There are various awards for the number of books children read, as well as for creative book reviews and follow-up work.
Ms Sturgeon announced the expansion of the challenge during a visit to Prestonfield Primary School to mark the 20th anniversary of World Book Day.
She said: "The First Minister's Reading Challenge has been a fantastic success since it was launched last year, with almost three quarters of schools across Scotland taking part.
"Reading is one of life's greatest pleasures, and the Reading Challenge is opening up a world of adventure and fun for young people as well as giving them vital literacy and language skills."
Prestonfield Primary head teacher Fiona Murray added: "The children love taking part in the First Minister's Reading Challenge and have read a far greater number of books as a result and really pushed themselves to tackle more challenging texts.
"We do lots of buddy reading in school where older children regularly read together with younger children. These opportunities not only encourage a real love of reading and improve literacy but also help children form positive relationships, build confidence and develop a sense of shared responsibility."
A challenge encouraging Scottish children to read is being extended to reach an extra 173,000 school pupils.