This sounds like your son might have allergic rhinitis and likely swollen sinus turbinates and adenoids. He is snoring because of his blocked nasal passages and narrow airway.
He is likely a mouth breather that would aggravate the situation and narrow the airway further.
This can lead to obstructive sleep apnea and lack of oxygen at night, which in turn can lead to poor quality sleep, disruptive sleep and daytime tiredness, poor concentration and poorer school results. He would need an ENT consult and assessment soon.
