The answer is that there is no magic involved, just the careful application of professional skills that are common to all good teachers - awareness of individual needs, excellent knowledge of the curriculum and a terrific grasp of how to make the plans that bring everything together.
It is also necessary that the leadership is not overawed by government guidance.
"We run a topic-based curriculum," says Ms Porter. "We don't adhere strictly to the Qualifications and Curriculum Authority schemes. We pick and dip among them and adapt them.
"Everything is always single year-group, so when the literacy strategy came out we all got together and completely redesigned it. We included all the main objectives, of course, but combined them into units that we could teach to three year-groups."
The approach to maths is similar, although here the school relies heavily on the mixed-age units derived from the strategy published by the Cumbria numeracy team on the website Cleo (Cumbria and Lancashire Online, two counties that have plenty of small, rural schools).
It is evident that Janet is extremely well-organised. She described the sequence of interlocking events by which she and her teaching assistant enable the three year-groups to work, sometimes as single-age groups, sometimes as two, sometimes as one. In this way, for example, Year 6 can have French, and more advanced work in core subjects. (Year 6 has an hour of maths on their own on Fridays).
"The younger children get a taste of the harder work," she says. "I differentiate the questioning, but the younger ones like the challenge of trying to answer."
The same message comes from head Jenny Dixon at the 36-pupil Armathwaite first school, in Cumbria. Although there are only two classes, as a deliberate policy they are taught by a team of five part-timers. The gains are in flexibility and the opportunity to use teacher specialisms in a personalised curriculum.
"You don't think of them as Year 1 or Year 2," says Ms Dixon. "You think of what the next step is for each child. Small schools are good at that."