Members of Australian chart-topping boy band 5 Seconds of Summer have come a long way since entertaining a few hundred students and their families at their school's Senior Soiree.
Their single She Looks So Perfect debuted at No.1 in Britain last week, and reached top spot in Australia and New Zealand. Billboard has tipped the song to go straight to No.1 in the US this week, and their concert tour of Australia next month sold out in minutes.
Music teacher Adam Day, who taught Calum Hood, Luke Hemmings and Michael Clifford at Sydney's Riverstone's Norwest Christian College, says the difference between their last school performance and what he saw on stage just a few months later was astonishing.
''The last time I saw them perform live for the school was for the Senior Soiree in 2012,'' said Day, who took a big hand in encouraging and mentoring the young musicians.
''They were confident and well-performed, but nothing as out there as what they are doing now.
''I was stunned when they came on stage in Sydney. They were just different boys with thousands of screaming girls in front of them.''
Day recalls three talented but painfully shy youngsters who had to be pushed to perform. ''I started teaching them music in year 7, and they excelled in all the practical activities of music but were very quiet and shy and reserved - they were very much closet musos,'' he said.
''I wrote on their reports back then that it would be good to seek performance opportunities to develop their confidence. They've certainly done that - more than any other student I've ever said that to!''
Fame came knocking for the trio when they were joined by drummer Ashton Irwin and began posting covers of Blink 182 and Justin Bieber songs on YouTube.
Their big break came last year when they toured with megastar boy band One Direction, playing stadiums around Britain, North America and Australia in front of hundreds of thousands of fans.
Despite their reticence about performing, Michael Clifford in particular made no secret of his ambition. ''Michael always said to me, 'I'm going to be a superstar one day','' Day said. ''That was his dream from year 9 on. I remember him coming off-stage from a performance night one evening and he said, 'Yeah, that's what I'm going to do. I'm going to be famous one day. Watch out.'''
Day said 5 Seconds of Summer stood out from many of the other boy bands because they were competent musicians in their own right.
''They're highly accomplished in what they're doing, mostly in guitar,'' he said. ''They don't just dance in front of a backing track. They're really skilled on their instruments.''
It's all still a little hard to take in for Day, who now teaches at a Christian college in Taree.
''I can't drive to school without hearing them on the radio now,'' he said.
''It's quite bizarre to hear your students on the radio. I can see the road they're on, and I think they'll go right to the top. I wouldn't be surprised if they're able to make it in America as well.''
With worldwide fame comes plenty of pressure but Day is confident the boys will not let it go to their heads.
''At school we tried to teach them a lot of values, and I really hope they can remember them and are able to keep a good life balance.''
- FFX Aus