The Intensive Fostering Service was launched by Kibble Education and Care Centre, in Paisley, as an alternative to residential care for young people from troubled backgrounds.
To show their gratitude, a number who are still being looked after by IFS carers sent the agency cards to mark a decade of operation.
One said: "IFS gave me a great and loving family to stay with.
"They've also turned me on to the right path so I don't make bad choices. They have turned me into a man and helped me grow up big time."
Another message read: "Thank you IFS for helping me through my highs and lows and offering me a great amount of support.I couldn't ask for a better family and they can't do enough for me."
In the past 10 years, the agency has placed 36 young people between the ages of five and 18 with 26 full-trained and approved carers.
Some have gone on to university, held down apprenticeships and worked in social care.
Kieran, 17, has been looked after by a carer for almost seven years.
He said: "Being in foster care has turned my life around and it has made me more mature and sensible.
"I had come from a dodgy background and I can't tell you how many times I got in trouble with the police with under-age drinking, vandalism and doing stupid and daft things.
"But being in foster care has made me want to stop behaving like that. I want to be a better person and have respect for other people so they have respect for me.
"If it wasn't for Kibble's fostering service I would still be getting into trouble and probably be locked up."
One of the first carers was 51-year-old Tommy Arthur, who says the fostering service has changed the lives of carers just as much as the young people being looked after.
He said: "You have to go on a journey with them that often involves supporting them to come to terms with their past abuse and losses in their lives that can be painful for them and painful to watch.You have to give an unconditional commitment that goes beyond liking children.
"However, seeing them come through the other side and flourish in your care makes my career so worthwhile.
"At the end of the day, I know I have truly made a difference to the lives of young people, but fostering has changed my life as much as those of the young people I have cared for."
Kay Gibson has been IFS operations manager since the service began. She said: "I am inspired every day by the dedication and commitment of the carers and I am so proud of the young people who have overcome adversities in their lives."