The union left discussions on Thursday, in a move that was blasted as "beyond unhelpful" by Higher Education Minister Simon Harris.
An ASTI spokeswoman said: "At subsequent engagements with the Minister for Education and her officials, the ASTI raised its concerns about doubts that had been put forward regarding the staging of additional component elements of this year’s Leaving Certificate examinations and the consequent relegation of the Leaving Certificate to a secondary position.
"On that basis, the ASTI believes that doubts regarding the staging of additional component elements of this year’s Leaving Certificate Examinations have been substantially alleviated. We expect the Minister to ensure that they will take place.