I will describe a recent observational project aimed at understanding the formation of multiple stellar populations in star clusters. Using moderate-resolution VLT/FORS2 spectra of stars in the intermediate-age clusters NGC 1651 and NGC 1751 in the Large Magellanic Cloud, we have found that the complex age structure known from precision photometry is matched by complex light-element abundances. This result carries important new implications for the formation of star clusters in various galactic environments.