Headteacher Alex Thorp introduced the mixed classes at Dunrossness Primary after the summer break, having seen the idea develop in England, where she used to work.
Despite initial scepticism from parents, particularly about the impact on P1s, it has been a big success, and Mrs Thorp has welcomed an "endless stream" of visitors from other schools and local authorities keen to see the idea in action.
The headteacher stressed, however, that mixing children aged three to five was merely a basis for more fundamental changes: centring learning on play and individual needs, which reflects key principles in A Curriculum for Excellence.
Mrs Thorp believes the scene that greets visitors is striking: "What's very different, especially for the P1s, is that you rarely see whole classes sitting down at the same time. Far more children are doing activities in different areas - things are very busy. Everybody is doing something all the time."
The mixed sessions mean a very able pre-school child can try P1 work, while less able P1s can do tasks suited to their abilities without fear of standing out. Less mature P1s, meanwhile, are benefiting from the emotional support of younger children.
Mrs Thorp said: "It's far more concentrated on what children need, rather than trying to get them to fit to our plan. It means they are that much more motivated and switched on.
"The teachers feel they have been given the go-ahead to use their skills and be more creative; it's putting the excitement back into teaching."
She stressed the mixed classes were "evolving all the time". It was found in PE, for example, that while a joint warm-up worked well, it was better to split the group thereafter, since P1s were ready for more advanced skills.
The school demonstrated a commitment to easing the move up to primary level this summer, when the majority of soon-to-be P1s were visited at home by a teacher and a nursery nurse. This allowed teachers to learn about a child's home setting and parents to ask questions. It also meant that concerns about issues such as toilet training were identified.
The transition was helped by physical changes to the classroom, as Mrs Thorp explained: "The children were coming into a setting that looked very much like their nursery, rather than being faced with lots of tables and the play stuff set on one side."
Mrs Thorp said that the attention to individual needs and the blurring of differences between nursery and P1 had had a remarkable impact: "This was the first year we didn't have any tears at the beginning of P1."
The Dunrossness way The school's 13 P1 pupils mix with 13 pre-school children each morning, before doing the same with nine three-year-olds in the afternoon.
Learning takes place in an area split by a wide doorway. The door is usually open, but can be closed if a noisy activity would detract from more quiet learning elsewhere.
There are two fully-qualified teachers and a full-time nursery nurse, sometimes joined by a part-time classroom assistant and a student nursery nurse; this means there can be as many as five structured sessions at one time, plus other activities in free-play areas.
The school's playground is divided into two zones: an area for children from nursery to P2, and another for youngsters from P3 to P7. This encourages P1s to look up to older children as role models, rather than spending all their time with younger children.
The mixed lessons are part of attempts to bring in more active learning for all of the school's 139 nursery to P7 pupils.