An analytic model of dustball meteoroid ablation is developed and used to generate synthesized Leonid meteor light curves. The model light curves are compared against observational data collected during the 1998, 1999, 2000 and 2001 Leonid outbursts. A power-law distribution of the form is assumed for the fundamental grain mass distribution, and we find that provides a good description to the typical Leonid meteor light-curve morphology, although the range is required to explain the entire gamut of observed light curves. We find an interesting discordance between the light-curve morphologies derived for the 1998 and 1999 Leonid returns; the former light curves being best described by , the latter having and being noticeably more rotund in shape. We suggest that the 1999 Leonid meteoroids were relatively rich in larger-mass fundamental grains. Since, however, both the 1998 and 1999 returns were composed of material ejected from comet 55P/Tempel-Tuttle in 1899, it is suggested that some form of orbital ‘sifting’, based upon meteoroid structure, has occurred. In addition, we find evidence for the existence of dustball meteoroids that are much richer in larger-mass grains than a simple power-law model would predict. Such dustballs may be clustered assemblages produced by accretion in the near-cometary nucleus environment. We find no clear correlation between Leonid meteor light-curve morphology and streamlet age, indicating that fragmentation, ‘weathering’ and thermal cycling effects are apparently not important for modifying Leonid meteoroid structure on time-scales of the order of at least several hundreds of years. [ABSTRACT FROM AUTHOR]