"This had a number of evaluation challenges included developing a single tool that could be used for every single young person who walks through the door of this organisation," Ms Bailey said.
The report tracks the health outcomes for over 300 young people seeking social and health assistance from the KYS service.
Health Minister Jonathan Coleman, who officially launched the report at KYS on Thursday, said "The findings show that over a five month period, 90 per cent of young people using the KYS service maintained or improved their health and wellbeing.
"These are positive numbers which reflect the contribution KYS is making.
"We know the importance of making health services for young people accessible and relevant to their circumstances.
"It is important young people have the right support at the earliest opportunity."
He said KYS was one of 11 Youth One Stop Shops supported under the Prime Minister's Youth Mental Health Project.
Budget 2014 invested $8.4 million over four years into the Youth One Stop Shops. This funding comes on top of the $600,000 committed in Budget 2013.
Ms Osborne said the model would ensure "our approach continues to be the best it can be".
KYS provides free physical and mental healthcare, and social services to about 4700 young people aged between 10 and 24 across several locations in Kapiti.