He brightens visibly at the idea of striding round his school, showing it off to visitors and seeing the children in action.
No wonder. Mr Kelly is fiendishly fit - qualified to take children, canoeing, kayaking, mountaineering and climbing - and likes to get himself and his pupils outdoors often.
But Garnteg is a school worth showing off: a low, hexagonal stone building opened in 1995, with a magnificent view across the valley and grassy slopes leading down to a wetland area designed by the children.
On another side is the latest addition to its facilities: a 40-foot high climbing wall, the first of its kind at any primary school in the UK. The pound;60,000 wall, funded mostly by a Lottery grant, is "a marvellous way to develop pupils' self-confidence and team-work skills", says Mr Kelly, and provides a good opportunity for children and staff to work together outside the classroom.
Six staff at the school are trained to use the wall, which is sometimes used three or four times a day, either by Garnteg pupils or by children from other schools, community groups - and the Fire Service. Even the younger ones can climb along the lowest section.
Apart from the wall, children spend as much time as possible learning outdoors. Geography, history, maths, science - all pupils have at least one lesson in each subject outdoors each term.
Pupils do the weeding and planting in the school grounds and can canoe, kayak or climb every week after school. To say nothing of Friday night sleepovers in school once a term and residential weekends in the Brecon Beacons... The 150 pupils need every extra chance. The school serves a fairly disadvantaged catchment area. More than one-third of pupils qualify for free school meals and a quarter have special needs.
Inspectors last year singled out "the range and provision of extra curricular activities" as "an outstanding feature and a great strength of school life". They said it was "a good school operating at the heart of its community" and it is continuing to improve.
The inspectors were not always so complimentary. When Mr Kelly arrived at the school in 1998, it was in special measures. Attainment was low and pupils' behaviour was poor. He quickly set about creating a working environment, setting parameters for behaviour and outlining expectations to children and parents. He did not change staff but helped build their confidence by using a team approach.
Now, he says, pupils' behaviour is "splendid" and attendance is good - 95 per cent last year, up from 89 per cent when he first arrived.
Vandalism has virtually disappeared since the children became responsible for the school grounds, he says. When some children were damaging the bowling green by riding their bikes over it, he invited the club to the school to teach bowling, so that the children could see why they needed flat grass.
But Mr Kelly does not think outdoor activities are good just for behaviour and team-work - they are the best setting in which to learn. A self-described "kinaesthetic learner", with a BEd and MEd in environmental sciences, he asks: "How can we live in a beautiful glaciated valley, with two rivers and notable peaks, showing man's land use and habitation patterns for 3,000 years, and sit our children on a piece of plastic in the classroom to study it?"