The government should use the revamp of the curriculum and exams to scrap the "outdated" Christmas leavers system, directors of education and secondary heads urge.
They want pupils to be able to leave after four years of secondary education, regardless of whether they have turned 16.
The Christmas leavers' system - under which pupils are obliged to return to school in S5 if they have not yet had their 16th birthday - was introduced as "a sop" to those with late birthdays when the school leaving-age was raised to 16, according to three of the most senior directors of education in Scotland.
But the practice is "outdated", and forcing youngsters to return benefits neither them nor the schools they attend, they argue. "If they've done four years, that's plenty," said Ken Cunningham, general secretary of School Leaders Scotland. "Forcing them to be in school is a frustration; they are disenfranchised, disenchanted and biding their time."
There are no exams that pupils can sit between August and December, said West Lothian's director of education and cultural services, Gordon Ford. They might attain a few modules in the first months of S5, but it would be more beneficial if schools helped them to move on to further education, employment or training, he argued. "It is hard to justify forcing children who have already undertaken four years of secondary education to stay for a further period, simply because of their birth date," he said.
The focus should be not on age, but on achievement, through the introduction of a "leaver's certificate" for those finishing after four years in secondary.
Leslie Manson, Orkney's director of education and vice-president of the Association of Directors of Education in Scotland, argued that children should start school slightly later, ensuring they are 16 by the end of S4, or the law should require them to complete seven years of primary education and four of secondary.
Bruce Robertson, director of education, learning and leisure in Aberdeenshire and a past-president of ADES, said: "While we are having a major review of education from 3 to 18 and the associated qualifications, we should also rethink this somewhat outdated practice."
The Scottish Government said it had no plans to release pupils after four years of secondary, regardless of age. "Most young people stay on beyond the end of S4 and we hope that even more will do so in future," a spokesperson said.
Changes to the S4-S6 curriculum would make it more flexible and better suited to individual needs, she added. "The Government recently launched its new model for post-16 learning - 16+ Learning Choices - which will ensure all young people of this age have a suitable offer of learning. This is vital to helping us improve the skills and life opportunities of those who leave school at the earliest opportunity, often with no - or minimal - qualifications."