St Mary's BNS dates back to the very early days of national schools, when an application was made in 1833 to the Commissioners of National Education for a Boys' National School. The school was situated for most of its first 130 years between St Mary's Church and the girls' school, and catered for boys from Second Class up only. Younger boys went to the convent school next door, and made their First Holy Communion in First Class before they transferred over to the big boys' school!
In 1965, a brand new building with 5 classrooms opened here beside the Liffey, with about 100 pupils from Second to Sixth Class in its first year. As the population of Lucan grew, so did the school. In 1974, when the main building opened, boys were taken into Junior classes for the first time. In 1981, the extension at the back of the main building was added to help cater for 900 pupils! Since 1992, the school has a steady enrolment of about 500 pupils.