But order is swiftly restored - classes are shuffled, the school day moves on. And the helmeted men?
"They're building our new integrated centre - it's the first in Newport,"
says Mrs Jones. "It's going to provide a range of education and care services for young families - breakfast clubs, after-school clubs, activity groups from0 to 3-year-olds, and also family support and learning, adult education, and much more."
"It's for children to have a flying start in life, and that means we need to be working with parents to help them give their children that start. A survey a few years ago found this area had the highest incidence of child poverty in Wales (two-thirds of Duffryn pupils qualify for free school meals). But things are getting better here."
There can be little doubt that Duffryn infants, with 130 pupils, is one of the instruments of that change. Four years ago the school started a nurture group for children with severe emotional or behavioural problems.
"These are the children who, unless there is an intervention, cannot access the curriculum," says Ms Jones. "I often think it's like they have so much cotton wool in their heads because of the problems of their day-to-day lives. But once you make children feel secure and happy and accepted, the cotton wool starts to disappear."
She admits that she'd initially been worried by the reaction of parents, sometimes from amongst those hardest to reach - "but they are just so pleased that those children are being looked after and given some self-esteem."
There's similar parental interest in another early intervention programme the school runs, the reading recovery group. Each day, eight non-readers in Year 1 will have a one-to-one session with a specialised teacher for up to 20 weeks -initially expensive, "but it saves so much money in the long run".
Mrs Jones is intensely proud of her school and its staff, particularly as they're one of 22 in Wales piloting the foundation phase, which will bring together early years and key stage 1 in 2008. It will be a "doing"
curriculum, with a strong emphasis on activity and structured play.
She's a great enthusiast for the change, although she knows that word play frightens some adults.
"But play is what children do in order to learn. Through that they can become competent, confident, and are ready to read and write - it's appropriate learning."
"Speaking and listening are the most important parts of communication. We have to get that right first."