The 18-year-old Royal Belfast Academical Institution pupil said he wanted to set himself a challenge when he selected a formidable seven subjects for A-Level – because he found it hard to restrict himself to the usual three choices.
For the last two years, Alastair has been studying biology, chemistry, physics, maths, further maths, Latin and Greek. Because of the lack of expertise here in Greek, he spent hours teaching himself.
Alastair got a $64,000 scholarship to attend California's Stanford University, his first choice university, which is known for its expertise in teaching sciences.
It followed disappointment at the end of last year, when Oxford University rejected the straight-A student.
Shane Johnston – the 'Inst' head of science – described the young pupil as a natural scientist who always waited for other pupils to answer a question before he would volunteer a response himself.
Mr Johnston's first memory of Alastair dates back four years to when the then-Year 10 pupil stood up in class and sang the periodic table song, listing the chemical elements without hesitation.
"Alastair is like a sponge. He's a natural, hard-working scientist, who will go beyond the chemistry and is very good at applying what he has studied," Mr Johnston said.
"He took part in the BT Young Scientist competition when he was in Year 11.
"He had read about the properties of a coffee plant and that it is a natural pesticide.
"So he carried out an investigation and tested the effects of caffeine on barley. He found that different levels of caffeine killed the barley.
"At the age of just 14 or 15, that's quite an achievement.
"Alastair also took part in the International Chemistry Olympiad in Russia this year, where he was competing with the best in the world."
The straight-A student told the Belfast Telegraph that there really was no secret to his success.
"I did not say 'I'm going to do three hours a day' or anything like that.
"I just did as much as I needed to until I knew as much as I needed to know," he said.
His former teacher described Alastair as a quiet boy with a quick, dry sense of humour.
"I have thoroughly enjoyed the last four years working with Alastair and his classmates.
"They get involved in everything and challenge you as a teacher.
"It's been all about team work," Mr Johnston added.