This study analyses the relationship between a firms' growth and the educational diversity of their workforce. It differentiates itself from other studies by using two measures of human capital diversity--one for education levels and one for fields--instead of one. The results show that workers with more diverse specializations than the workforce of competitors benefit the firm's growth and extensive margin of trade. Contrastingly, above-average workforce heterogeneity in education levels does not seem to affect firms' performance. Furthermore, it is shown that the association between human capital diversity and firms' performance differs among sectors. Compared to previous studies, which concentrated on one particular industry or one measure of educational diversity, this more comprehensive approach allows reconciling some of the contradicting results. The study shows that the mixed results in existing papers can result from dissimilar impacts of various measures of human capital diversity on firm performance or its differences among sectors.