His early education was under Bernard Gilpin, the 'Apostle of the North', at the Royal Kepier Grammar School in Houghton-le-Spring, Durham.
Here he won a reputation as a poet and orator, and a skilful disputant in theology, well read in the Church fathers and schoolmen.
Here he protested against the adoption of the thirty-first article of the Belgic Confession, which affirmed 'that the ministers of the Word of God, in what place soever settled, have the same advantage of character, the same jurisdiction and authority, in regard they are all equally ministers of Christ, the only universal Bishop and Head of the Church.'
Carleton maintained the doctrine of apostolical succession in opposition to this levelling article; his protest was ineffectual.
When the English deputies returned home in the spring of 1619, the Dutch States, besides paying the expenses of their voyage and presenting each with a gold medal, sent a letter to the king in which commendation is made of Carleton as the foremost man of the company and a model of learning and piety.