A small minority of Irish students attend fee-charging second-level schools. However, media analyses of the backgrounds of those students who go on to more sought-after tertiary educational institutions or degree courses suggest that a disproportionate number of them were attendees at fee-charging schools. There are a few reasons why this might be the case. In this analysis, the longitudinal data points of the Growing Up in Ireland (GUI) study are exploited to weigh up the evidence behind differing explanations. An estimated measure of Leaving Certificate success was generated for 3105 participants in wave 4 of the GUI. From waves 1 and 2, the ability of those participants was calculated based on their performance in several standardised tests taken prior to attending second-level school. The analysis found that while the students who attended fee-charging schools were about 9% ahead in Leaving Certificate performance, they had roughly the same lead in measured ability on entry into the second-level schools. The analysis found a significant but marginal positive effect on attending private schools. This result is in line with the general international findings. Ireland's hybrid funding structure for fee-paying schools is discussed. Gender and household income effects were noted.