Schools are being warned against undermining reforms aimed at raising high school standards by allowing students to choose easier courses.
In a blunt letter to principals last month, the School Curriculum and Standards Authority said schools could be directing Year 10 students to Year 11 and 12 courses designed only for those who fail minimum reading and maths standards.
It said schools might be asked to explain their enrolments.
"It has come to our attention that some schools may seek to enrol students in courses for which they are not academically suited and in which they are not eligible to enrol," it said.
Under reforms to take effect for Year 11 students next year, most will choose between ATAR courses, which qualify them for university, or general courses which lead to a vocational certificate.
Students who fail online literacy and numeracy tests in Year 10 are eligible for foundation courses and those with intellectual disabilities can do preliminary courses.
The letter said a key reason for the reforms was that too many students had been choosing the easiest course options under the previous system.
"The foundation courses are not designed to be an alternative senior secondary pathway," it said. "It is also concerning to hear that some schools are considering enrolling students in preliminary courses to avoid the requirement to sit the online literacy and numeracy assessment."
Authority chief executive Allan Blagaich said the letter came after questions from schools which were counselling students on course selections for next year.
"The heart of these reforms is about what's best for students and to ensure they're appropriately challenged," he said.
Education Minister Peter Collier said the previous system let too many students take easier options and it would be a concern if schools sought to circumvent the intent of the new structure.