school years and ages

For example, if your child reaches compulsory school age on 31 March, they must start full-time education at the beginning of the next term (summer term that year).
Contact the local council or school to ask for your child to start later. They’ll decide if your child should start in reception year or year 1, based on what’s in the best interests of your child.

Republic of Ireland Class Groups
Age in Years

Age 11–14. Y7–9. 1st–3rd form secondary
Age 3–5. Y0. Nursery / Reception (Early Years Foundation Stage)

References:

http://www.rathdownschool.ie/Class-Ages/
http://prosperoteaching.com/from-overseas/uk-key-stages-by-age-year/
http://www.gov.uk/further-education-courses