Keir Bloomer, who helped devise Curriculum for Excellence (CfE), which was introduced in 2010, said Scottish schools were “in grave danger of minimising the potential of a generation of our young people” by narrowing subject choice on a random basis.
The think-tank Reform Scotland’s Commission on School Reform, chaired by Mr Bloomer, has previously published evidence showing the number of exams pupils can take in fourth year is dropping, with subject choices becoming dependent on where young people go to school, rather than their ability.
Most state schools have cut the number of subjects on offer, whereas no private school has.
Mr Bloomer said: “CfE was supposed to broaden education and opportunity, but it is becoming increasingly clear that its implementation is narrowing it.
“We are seeing a postcode lottery where pupils who are capable of successfully sitting eight exams are being prevented from so doing.
“This is narrowing their education and limiting their prospects as they move towards Highers and then to college or university.”
In 2014, as part of CfE, the Standard Grade exams system was replaced with National 4s and 5s. While Standard Grades were taught over S3 and S4, National 4s and 5s can only be studied in S4.
The concept of Broad General Education (BGE), previously studied in S1 and S2, was extended up to the end of S3.
However, Reform Scotland says that this change to a single year of study has enabled pupils to sit a maximum of only six National 4s and 5s, rather than eight.
Mr Bloomer said: “The Scottish government must put an urgent stop to this by making it clear to all schools that pupils may sit eight exams, and that BGE can once again cease after S2. They can do this temporarily until they get a grip on what is going on here, but do it they must for we are in grave danger of minimising the potential of a generation of our young people.”
A Scottish government spokesman said: “This analysis takes no account of differences before and after the introduction of CfE, which helps equip pupils with the knowledge, skills and attributes needed for life in the 21st century.
“It means pupils learn a wide range of subjects up to S3. Schools then have the freedom to design a set of courses, qualifications and awards between S4 and S6, tailored to meet young people’s needs.
“What matters is the qualifications that pupils leave school with and last year a record proportion went on to positive destinations including work, training or further study.”