Fifteen students at the English Schools Foundation's six schools have scored top marks in the International Baccalaureate diploma exam.

Some students said on Monday they were not expecting to attain the full mark of 45 even though their predicted score was just that.

Yashasvini Agarwal described the moment when she found about the results.

"I was so nervous," she said.

"We were actually recording the results. We opened them subject by subject.

"And after each subject, we just screamed for a solid minute. So we had lots of screaming."

It was a dream come true for Kristie Lo.

"Getting 45 [marks] was kind of my childhood goal since year seven," she said.

"So for me, for the past seven years, I feel like I've been trying to work towards this goal.

"Honestly, I was just hoping for the best.

"The moment I saw my result, I was really relieved that all my hard work did not go to waste and I could finally achieve the goal I had since the start of secondary school."

Another best scorer, Kush Zingade, told RTHK that he did not have just the pressure of exams to deal with.

"It's become a tradition where I become sick before every single exam or test," he said.

"I was really stressed for my first exam, which was physics, because I was sick and coughing and my mind wasn't in the right head space.

"Physics was a great struggle for me in that regard because I was dealing with health [issues] and also the pressure of exams."

Unlike a majority of top scorers who hope to become a doctor, Zingade plans to study computer science at Boston University in the United States.

"I think when we look around, especially in Hong Kong, being sort of a technological hub in Asia, there is technology, computers, they're everywhere," he said.

"And I just really want to try and enable myself to be able to interact with them."

The ESF's director of strategy and communications, Rob Shorthouse, was pleased with the results.

"I think the results that we are seeing today are absolutely incredible," he said.

"To achieve top scorer in IB is such an extraordinary achievement that students have to work so hard in order to achieve what they have today.

"And we just couldn't be more proud of them. It's an exceptional set of results."

Shorthouse added that the average score of ESF students was 36.1 this year, compared to the global average of 30.3 last year.