Hands-on science typically uses physical materials to give students first-hand experience in scientific methodologies, but the recent availability of virtual laboratories raises an important question about whether what students' hands are on matters to their learning. The overall findings of two articles that employed simple comparisons of physical and virtual materials suggest that virtual materials could be an effective and efficient alternative to physical materials when teaching with explicit instruction and discovery learning methods. (This paper is a summary of Klahr, Triona, & Williams, 2007 and Triona & Klahr, 2003.)