After Slovenia seceded from Yugoslavia in 1991 many nationals from the former Yugoslav republics stayed behind, whose native language was not Slovene. In 2009 every eighth resident of Slovenia was born abroad, and therefore an immigrant. This data gives us the basis for our research question. Are the achievements of (1st and 2nd generation) migrants in reading, mathematics and science performance, when compared to the achievements of native speakers statistically significant? Which are the secondary school programs in Slovenia that show the greatest differences? We will address these questions with analyses of the data of the Slovenian sample for PISA 2006. All data will be statistically analysed with SPSS (Statistical Package for the Social Sciences) and the special module Replicates, which allows for the calculation of standard errors, means etc., when not using simple random sampling. We use weighted databases, with weights corresponding to the PISA 2006 study. Data will be presented using descriptive statistics, bivariable analysis (correlations) and multivariable analysis (regression analysis). We assume that native speakers have significantly higher achievements than 1st and 2nd generation migrants, especially in upper-secondary educational programs. We will try to explain the results through different demographic backgrounds of students.