Background: An in-depth understanding of the process and products of evolution is an essential part of a complete biology education. Phylogenetic trees are a very important tool for understanding evolution and presenting evolutionary data. Previous work by others has shown that undergraduate students have difficulty reading and interpreting phylogenetic trees. However, little is known about students' ability to construct phylogenetic trees. Methods: This study explores the ability of 160 introductory-level biology undergraduates to draw a correct phylogenetic tree of 20 familiar organisms before, during and after a General Biology course that included several lectures and laboratory activities addressing evolution, phylogeny and 'tree thinking'. Students' diagrams were assessed for the presence or absence of important structural features of a phylogenetic tree: connection of all organisms, extant taxa at branch termini, a single common ancestor, branching form, and hierarchical structure. Diagrams were also scored for how accurately they represented the evolutionary relationships of the organisms involved; this included separating major animal groups and particular classification misconceptions.