"The 38-degree heat there affected my results a little against some of the top girls in Australia," says the Year 12 pupil.
Adding to the achievement was the fact the Aussie winner won gold at the age-group world championship last year.
Jamieson finished fifth in the 70km road race, which went twice round the undulating course.
"I was in a leading breakaway bunch of five with another group 10 minutes behind," she says, adding a 1.5km hill climb sorted the girls from the women, as it were, in a field including four other New Zealanders.
Bike NZ sent 10 riders to the champs - a five male/female split.
Maddison Farrant, a Kiwi, finished eight seconds ahead of Jamieson in the road race but the latter says "technically I finished first" because the Waikato rider is in her second year as an under-19 competitor.
The CHB rider was the only Kiwi not in a national development squad.
"Hopefully next year I'll be back there with some good results," says the teenager who Dylan Stewart, of Napier, has been coaching for the past two years. A fortnight ago, Jamieson won the gruelling Mangatainoka bush tour, clocking 2hr 37min.
The next female rider was about four minutes behind in the field of 163, which included elite senior campaigners.
Jamieson's entire family in Waipukurau are members of the CHB club.
Parents Glennis and Wayne enjoy the challenge while sister Ella, 12, recently returned from the nationals.
Amanda Jamieson hopes to be a member of a professional cycling team overseas some day.
"Cycling keeps me busy," says the youngster who hopes to pursue a university degree but isn't sure what it is just yet.
Fellow CHB College pupil Corbin Mason-Smith finished seventh in the boys' time trial and 10th in the road race in Toowoomba. The 17-year-old national development squad member was a little disappointed with his time trial.
"When I went on to the course [for the time trial] I was feeling as good as when I was training," Mason-Smith says.
The Year 13 pupil hopes to be among the top three at the New Zealand nationals in Cambridge in May after the time trial.
"I also want to be in the top-five podium in the New Zealand touring points series."
A competitive rider for six years, the son of Emma and Aaron reckons CHB produces a rash of elite competitors because of Cycling CHB's sound junior programmes.