Visit their classrooms at 9am and you are blinded by the reflected light from their clothing, as if you had stumbled into an audition to advertise the detergent that washes whiter than white.
Visit two hours later and the scene is transformed. After a 20-minute break and an encounter with the playground, mother's pride is replaced by Fagin's urchins. The shirts are stamped with black ball marks bearing witness to "chesting" skills, while unaffected patches are used for cleaning the ball or wiping hands - note the order of priority. A fall in a puddle is an optional, and spectacular, extra.
My enquiries about mothers' reactions when the shirts return home are met with puzzled shrugs. The long-suffering mothers have learnt that remonstrations fall on deaf ears and that recourse to the washing machine is easier. Their dedication ensures that the following morning begins with the usual sparkle. Their sons may not notice their efforts but I do.
Pity our primary 7 mothers who also have primary 4 sons because they show signs of challenging for the "dirty" Oscar this year. Their speciality is heading the ball just after it has rolled through a deep puddle, thereby ensuring black, matted hair and faces striped with rivulets of dirt.
Just as well for all of us that each of these boys has a good woman at home patiently prepared to set them anew on the path of cleanliness and respectability, day after day.
The effect of the good woman has featured in my recent thoughts as we have been enrolling children for next year's primary 1 classes. I am used to having former pupils as parents and seeing how the child has grown into the adult, but this year's enrolment season brought unexpected pleasure in the return of several former pupils who had disappeared from my ken many years ago.
As children, they came from homes where circumstances were difficult.
Through no fault of their own, the cards were stacked against them and anyone could be forgiven for predicting a troublesome future. Apart from one, they sent impressive wives or partners to the enrolment with the message: "Say hello to Mr Toner." The other came himself and, at the age of 26, still calls me "sir".
The delightful conversations established what they had in common and what had helped them overcome early difficulties: a steady job, a settled home life and, most evidently of all, the love of a good woman. Schools set targets for all activities, as if the lives of our pupils depend on them.
For the boys, the love and care of a good woman is probably a more important influence.
The mothers of our dirt champions don't complain to me. If they did, they might receive the answer I apply to all current problems: "It will be all right when we move to the new school." But that's a lie. The new school will have grass, a winter horror that our patient mothers have so far been spared.
However, there is a glimmer of hope. One of our dirtmongers recently recounted a bus stop conversation with a well-remembered former pupil, a skilled footballer and leader of the pack, now a mature S2.
"Guess what," said my informant. "McKinnie says he doesn't play football at school now. He says it's all right to play football in primary and in first year but in second year you realise you don't want to walk around dirty all day."
"So who's the girlfriend," I asked. "Who's the good woman?"
Brian Toner is headteacher of St John's primary in Perth.