Size confers a crucial advantage, according to the latest A-level analysis in Northern Ireland.
Ulster's secondary-school league tables of results have just been released and show that large grammar schools out-performed their smaller competitors last summer.
The Northern Ireland grammar school average was 46 per cent compared with 36 per cent five years ago, according to figures just published by the Department of Education.
Large schools generally did better at A-level. Half the pupils in the largest 20 per cent of schools obtained three or more grades A-C. However, in the smallest 20 per cent of schools, only 39 per cent of pupils reached that standard.
This compares with between 58 per cent and 74 per cent of students at the big mixed schools such as Banbridge Academy, Sullivan Upper near Belfast, Rathmore and Methodist College in Belfast.
A few girls' schools proved the only exception to the rule. The small Bloomfield and Strathearn schools in Belfast and the tiny St Joseph's Convent in County Tyrone all scored well at A-level.
No boys' schools were in the top 10 at either GCSE or A-level. In fact, St Mary's and St Malachy's, the two boys' grammar schools in Belfast, were in the bottom 10, joining Cambridge House boys in Ballymena, which has been performing poorly for years.
At GCSE level, both secondary and grammar schools have boosted the proportion getting top grades by five percentage points since 1993. According to the department, 53 per cent gained top GCSE grades in 1997 compared with 45 per cent in England.
However, the tables are bad news for the high-profile Raising School Standards Initiative, which was set up to tackle underachievement in struggling Belfast secondary schools.
The initiative has failed to make any difference in the proportion of pupils getting either five or more GCSE grades A-C or A-G. The three pilot schools involved since September 1994 actually got slightly worse on both measures.
In fact, the Belfast secondaries that did not take part have improved their results.