Some parents and employers are likely to be "confused" about the new GCSE grading system, England's chief exams regulator has acknowledged.
Educating the public about the change is a "big job" that will take time, according to Sally Collier.
Under major reforms to exams, traditional A*-G grades have been axed and from this summer students will see GCSEs in English and maths graded 9-1 - with 9 the highest result. In the next few years, the changes will be brought in for all subjects.
Supporters have argued the move is necessary to allow more differentiation between students.
But there have been concerns raised over a lack of clarity about the new system, with one school leader warning that confusion could lead to pupils missing out on sixth-form places.
In her first interview as Ofqual chief regulator, Ms Collier told the Times Educational Supplement (TES): "I think there are more parents and businesses that need to know.
"Are they going to be confused? Probably. Is it a big job? Yes. Is it going to take time? Yes."
She suggested that schools and colleges will need to be open when setting their entrance requirements using the new grades, to ensure that they are accepting the right students onto the right courses.
"You want them to understand that they need to be flexible in setting their requirements so they don't accept kids that will struggle, or vice versa they are not rejecting kids that actually were fine," Ms Collier said.
"I think the biggest risks are (if) those that are using the new 9-1s for entrance requirements - whether that be a college, apprenticeship, or a particular course where these qualifications are used as entrance hurdles - don't understand them, or parents don't fully understand what their children need to get to their next stage, then that's the biggest risk."
Ofqual has begun a campaign to raise awareness about the changes, the TES said, including TV adverts and materials for schools.
Earlier this month, Geoff Barton, who becomes the Association of School and College Leaders' (ASCL) new general secretary on April 18, said more communication about the reforms is needed.
He told the Press Association: ''The confusion is caused by mixed messages from the Government and a lack of clear communication.
''On one hand, schools are going to be judged on the number of pupils who achieve a grade 5 or better in English and maths and in the EBacc (English Baccalaureate).
''On the other hand, the Government says that grade 4 is enough for pupils to progress to the next stage of their education if sixth forms and colleges decide it 'meets their requirements'."