The structure at Cahermacnaghten sits at the south-western corner of its townland, part of a small settlement that includes the remains of four other rectangular buildings, a kiln, enclosures, and a clochán, the last being a small dry-stone beehive-shaped dwelling typical of early Irish sites. The main building is substantial, measuring roughly 15.5 metres east to west and 7 metres north to south, with walls 1.3 metres thick. Its architecture is harder to place than those numbers suggest. The proportions resemble a parish church or medieval hall, and the east end carries a late medieval pointed doorway with half-roll and fillet moulding, a decorative profile associated with quality craftsmanship of the period. Inside, seven or possibly eight Tudor late Gothic windows originally admitted light; they were shuttered rather than glazed. Loft spaces sat above at least the eastern and western ends, reached by ropes or ladders. Four large wall cupboards, two in each gable, and a fireplace set into a partition wall complete a picture that is, to put it plainly, unlike any ordinary dwelling.

The excavation season of 2008 clarified what this building most likely was. Radiocarbon dating of animal bone from a primary occupation layer returned a date range of 1488 to 1603, placing the building's first use in the late fifteenth or sixteenth century. Researchers FitzPatrick, and later Clutterbuck and FitzPatrick, concluded that this was almost certainly the schoolhouse of the O'Davoren family, hereditary Brehon lawyers whose base at Cahermacnaghten was among the last functioning schools of Brehon law in Ireland. Brehon law was the native Irish legal system, codified over centuries and transmitted through professional legal families; by the sixteenth century, such schools were becoming rare under the pressure of English colonial administration. The three-roomed layout uncovered in 2008 fitted a teaching and study environment, and a small fragment of inscribed slate found in the western room, a single character on a thin, friable piece, was identified as potentially diagnostic of school activity. The building was later converted for domestic use, probably in the mid- to late seventeenth century, when a new fireplace and partition wall were inserted, likely during the occupation of Turlough O'Brien or one of his tenants. By the eighteenth and nineteenth centuries it had been largely abandoned, and in the twentieth century it served, finally, as an animal enclosure.