Structural problems were found in the fabric of the buildings.
Tyrrelstown Educate Together School and St Luke's, National School, Tyrrelstown were assessed today as part of a programme of structural checks being undertaken on schools built by Western Building Systems.
Both schools have since been closed with immediate affect. Over 1,200 children attend the schools.
The Department of Education released a statement explaining the situation in greater detail.
"Following advice from a consultant structural engineer, and in consultation with the school authorities, a decision was taken to close both schools with immediate effect."
"The Department is working closely with the school authorities in relation to interim accommodation solutions for the over 1,200 affected pupils.
"The target is to have interim accommodation solutions in place for when pupils return to school after the mid-term break next week. At all times the key priority of the Minister and the Department is the safety of pupils and staff.
"The Minister and the Department acknowledge the disruption that school closures have on families and parents, students and staff of the affected schools will be kept fully up to date with developments.
"The investigations at Tyrrelstown today, while not identifying any imminent danger, suggest that those two schools should close as a precautionary measure to allow for further detailed investigations at both schools.
"Further examinations of other schools built by Western Building Systems are ongoing.
"At all times, the Department remains in close contact with principals and the management of schools being inspected in order to keep them up to date with developments."
There is no estimated date as to when either school will be back up and running.
