In April 1843, Sewell and his friends Monsell and Todd founded at Stackallan House, County Meath,
St Columba's College, designed to be a sort of Irish Winchester and
Eton "and something more than Winchester or Eton." It was set in beautiful countryside. In 1861 the
Clarendon Commission defined it as a public school, but Sewell's aim was to provide an Anglican education for the ailing Church in Ireland, with emphasis on pastoral care and rigorous classical disciplines. The school was supported by the nobility and church. From Lord Boyne Singleton and Sewell rented the land with conspicuous approval from the Archbishop of Armagh, Lord
George de la Poer Beresford, the college's Governor. Sewell hoped to inspire boys
in locis parentis, giving them cubicles to live in and "strengthen, enlarge and purify their minds." With the classics they were to teach modern languages, modern history and mathematics, drawing, architecture and the Irish language. Sewell was disliked at St Columba's. Despite his trips to raise much-needed funds, his college showed bad faith towards a financial supporter who brought it much furniture and silver. His connections at Oxford, particularly
Magdalen College, were useful. Another substantial Sewell contribution was a large library collection. His colleagues wanted a more relaxed Irish Gaelic school, whereas he was known to have punished boys for failing to show table manners befitting young gentlemen. Cold showers and hard beatings were necessary, but Sewell believed the most dreaded exclusion to be from chapel. Emphasis on regular attendance at Evensong and Matins was central to his scholastic vision of a High Church interpretation of the
Book of Common Prayer. While he also gained a reputation for high standards of cleanliness and medical health. Singleton agreed with Sewell that there must be fasting and feast days, but this offended Irish Protestant sensibilities. The Fellows Lord Adare and
William Monsell converted to Roman Catholicism. In May 1846 he resigned with Warden Singleton to return to Oxford and Exeter College, having been outvoted by the Fellows of St Columba's. Singleton met in Turl Street to discuss the opening of another college. On 9 June 1847, he helped to found
Radley College, installing Singleton as Warden. Sewell's intention was that this school too should be conducted on strict High Church principles. Sewell was originally himself one of the managers of St Columba's, and later the third Warden of Radley, but his business management was unsuccessful in both cases, and his personal responsibility for the debts contracted by Radley caused the
sequestration of his Oxford fellowship. In 1862 his financial difficulties compelled him to leave England for Germany, where he remained until 1870. ==Reputation==