Kate, who is now six months pregnant with Prince George's little brother or sister, sported a navy blue Madderson coat with patterned fringing.
The radiant Duchess beamed and waved to the waiting crowds of youngsters as she arrived at the school to open The Art Room's ninth project, The Clore.
In her role as royal patron of The Art Room, an Oxford-based charity which provides art therapy rooms to help enrich the lives of disadvantaged children, Kate unveiled the colourful new space.
The History of Art graduate then took part in a round table discussion with education professionals, a child and adolescent psychiatrist, Clore Duffield Foundation chair Dame Vivien Duffield and artist Grayson Perry.
Kate and Grayson previously bonded over their love of art in February 2014 when they attended the Portrait Gala at the National Portrait Gallery.
Prince William's wife was clearly thrilled to have made the engagement, having previously sent her heartfelt apologies at having to cancel her appearance in October.
"I wanted to share my congratulations with you all for the launch of the new Clore Art Room," she said in a statement. "I was looking forward to joining you all for this particularly special day as part of The Clore Duffield Foundation's 50th Anniversary year.
"I am truly sorry that I cannot be with you all today as you celebrate this milestone," she added. "As patron of The Art Room I feel great pride to see the work that the charity is doing. Vulnerable children flourish in the safe havens that The Art Room provides; this highlights just how important it is to support children at a time when they most need help and support."