The length and structure of the school day is not currently specified in legislation but the curriculum for excellence operates on an assumption of 25 hours of teacher contact each week in primary schools.
Ministers now plan to amend the Education Bill currently before the Scottish Parliament to ensure a minimum of 25 hours with teachers per week for pupils.
The Government said it follows concerns raised by both teachers and parents about the possibility of children in some areas receiving less teacher contact time due to local council proposals for a shorter school week as part of cost-saving plans.
The plans will be tabled on Wednesday and considered by the Education & Culture Committee next week.
It would also allow ministers to put in place a minimum number of hours in secondary schools, the Government said.
Education Secretary Angela Constance said: “The Scottish Government is working with local authorities, parents and others to ensure our education system delivers both excellence and equity for every child.
“We are driving a relentless effort to boost educational achievement and, critically, to make quicker progress in closing the ‘attainment gap’, for example through the £100 million Scotland Attainment Challenge.
“Scotland’s teachers are absolutely critical to these efforts. That’s why we have committed investment of up to £51 million this year specifically to help local authorities to maintain teacher numbers.
“And it’s why we will legislate to provide certainty for pupils, parents and teachers about the length of the school week - a teacher time guarantee that every one of our children and young people should expect, and which they deserve.
“Decisions on the amount of time with teachers, in class and at school should always be made based on the potential educational benefit for children, rather than on how much money can be saved.”