The Math Olympiad results seems to indicate Sri Lankans are about comparable to Bangaladeshis in Math capabilities (Approximately 70th rank). We Sri Lankans seem to be doing far worse than India and Brazil (23 and 20 respectively). Sri Lanka has a Math Olyimpiad organization too and has quite a bit of information on the site http://www.slmathsolympiad.org/ . Complete results of the Math Olympiad since 1959 is available here.
Another interesting comparison is IQ. Again we do not seem to be doing any better than the Indians. One must keep in mind that the Math Olympiad is about selecting the best in a country. The National IQ measure is for the country as an whole. India with half its population being illiterate still has an IQ quotient comparable to Sri Lanka. Does that mean Sri Lankans are not as smart as we think or they are just smart alecs who cant be bothered with IQ tests. Steve Sailer comments that new study of Sri Lankan IQ is warranted because it is highly literate, low malnutrition, similar racial makeup with South India...and the only study we have is one way back in 1954 with a sample size of 46, that too on eight year olds, when IQ is not very heritable. The IQ of 79 for Sri Lanka is quite meaningless in the present context
There is an whole discussion on Indian IQ over here. This location has a summary of the Lynn and Vanhanen study of IQ and the Wealth of Nations. This is the wiki with data of the controversial 2006 book by psychologist Richard Lynn and political scientist Tatu Vanhanen IQ and Global Inequality