Proposals by North Ayrshire Council to raise the school starting age to six have been rebuffed by Education Secretary Michael Russell.
"These plans are not in line with legal requirements and as such seem ill thought out, with many of the critical issues not addressed," Mr Russell said.
It was not clear whether the council was proposing to move the entire period of compulsory education - including when pupils take exams and leave school - back by a year, or to cut the number of compulsory school years, he said.
The educational impact of any change would have to be carefully examined along with other issues as part of a much wider debate.
"Ministers therefore have no intention of altering the age at which a child in Scotland starts their school education," Mr Russell added.
National legislation would be required before any change could be made to the age at which children in Scotland start school.
Section 31 of the Education (Scotland) Act 1980 defines the period of compulsory schooling, identifying a person of school age as someone who "has attained the age of five years and has not attained the age of 16 years".
The council has also abandoned a proposal to introduce a four-day school week, following widespread objections. Both proposals were the result of officials being asked to come up with radical ways of making savings.
Council leader David O'Neill said raising the school starting age had been widely discussed by education professionals across the UK for several years and was therefore likely to be explored.
The North Ayrshire proposal received qualified backing from Bronwen Cohen, chief executive of Children in Scotland.
"Scotland is very much in the minority in setting five as the age for compulsory schooling and there are some sound educational arguments for starting later," she said.
"But if we were to do that, we would need to radically improve the access, hours and quality of pre-school services," she said.
Colwyn Trevarthen, emeritus professor of child psychology and psychobiology at Edinburgh University, said a move to raise the school starting age should only be supported "if it is linked to better provision before starting school - not just to saving money".
Giving young children informal, playful, collaborative learning with experienced teachers and peers would be a positive move, rather than "pushing them into formal instruction when they are at their imaginative and sociable best".