Victoria Williams, 29, collected her NPQH from education and lifelong learning minister Jane Davidson at an awards ceremony in Llandrindod Wells last week.
It was a double celebration for her school, Ysgol y Dderi in Llangybi, Lampeter, as colleague Iona Jones-Roberts graduated at the same time.
Another teacher at the 137-pupil school, Lilian Miles, is working towards the NPQH, while deputy head Mary Davies was among the first people in Wales to complete the course following its introduction in 1997.
And head Ann Davies has completed the Leadership Programme for Serving Headteachers.
Miss Williams, who trained as a teacher at Trinity College, Carmarthen, said she did not feel like the youngest on the course, because she had been given responsibility by her head and "different things to deal with".
"The most challenging thing was being confident in myself, because I didn't have that many years' experience and I was with deputy heads from big comprehensives," she said.
"The course gave me confidence, thinking I could discuss things with them in a group, and my opinion was important."
Head Mrs Davies said a key part of her role was to develop her staff as potential school leaders - "not just to make them better teachers".
"I wouldn't encourage them to do NPQH for the sake of it. But it fits in with how the school is run. They take on responsibilities and everything gets discussed as a team, and they become more confident.
"Victoria is young and she knows she's not ready to be a head yet. But in this part of the country there are many small schools, and you could be a teacher one day and a head the next."
She acknowledges that equipping her staff with the qualification they need to move on to other jobs could backfire.
"I don't want them to leave. Once you have worked on your staff you get very attached to them. But as a head, you can't be narrow: you are here to develop children but also to develop your teachers and make sure they enjoy coming into school and would go for better things."
The Ysgol y Dderi pair were among around 120 NPQH candidates collecting awards after successfully completing their courses in the past year.
Around a dozen, including Iona Jones-Roberts, had to fit their studies around childbirth.
Mrs Jones-Roberts, whose 23-month-old daughter Beca Mai attended the awards ceremony, started the NPQH four years ago while working at Rhydlewis primary, Llandysul, where the head was the only other teacher.
NPQH becomes a requirement in Wales for all first-time heads from this September.