Registration for the Leaving Cert opens today, with bosses insisting the site has be "stress-tested" to ensure it doesn't crash.
The new portal will allow some 61,000 students to sign up to receive calculated grades instead of sitting the exam.
The Leaving Cert was postponed this year due to the Covid-19 pandemic and students have been given the option to receive a calculated grade or sit the exam at a later date.
The online portal opened at 10am this morning will remain open until 10pm on Thursday.
Director of operations and IT at the Department of Education, Andrea Feeney, told Newstalk FM that the new online portal is a "one-stop shop" for students.
Ms Feeney insisted it has been stress-tested to prevent it from being overwhelmed.
She said: "We have done a lot of stress-testing and we have been working with our internet service providers to make sure that that doesn't happen.
"When the portal closes on Thursday, we will provide that information to schools so that the schools can provide an estimated percentage mark and a ranking of each of their students."
Students have to confirm the level of exam they would have sat, or they can change to a lower level.
Schools have been asked to assist their students as much as possible but if anyone has trouble getting access online, there will be helpline support from midday on Tuesday.
When registering on gov.ie/leavingcertificate, students must have their examination number, Personal Public Service number (PPS), email address and mobile phone number.
Education Minister Joe McHugh said: "Every school has been sent on the information to provide to their students so that they are able to complete the registration on the student portal.
"This is a brand new system that it has been necessary to introduce because of the decisions we have had to take as we respond to Covid-19 situation."
