Complex sentence: The Education (Welfare) Act, 2000 raised the age to the current minimum of 16 years, and prohibits under-18s from leaving school until they have completed three years of secondary education (i.e. up to Junior Certificate).
Split into simpler sentences: The Education (Welfare) Act, 2000 raised the age to the current minimum of 16 years. Those under 18 may not leave school without completing three years of secondary education (i.e. up to Junior Certificate).