Summary: We consider dynamic scheduling for batch-processing machines. Our research is motivated by the burn-in ovens found in semiconductor manufacturing. So far, research in this field mainly concentrated on control strategies that assume batches to be homogeneous, i.e. products should all belong to the same family. However, burn-in ovens may allow for simultaneous processing of alternative families of products. Families differ from each other with respect to product volume. We propose a new scheduling approach that addresses these situations. The objective is to minimize average flow time per product for the batch operation. Our so-called look-ahead strategy adapts its scheduling decision to shop status, which includes information on a limited number of near future arrivals. The potential of the new strategy is demonstrated by an extensive simulation study.