The purpose of this study was to develop and validate instruments that will assess the laboratory skills of students completing high school science courses. In each of the science areas (biology, chemistry, and physics), tests were developed around six laboratory tasks. Each test used a two-part format with a total time of 80 minutes. Students had to plan an investigation, collect and organize appropriate data, and formulate conclusions based on calculations and graphs. A different test was developed for 12th-grade students not enrolled in a science course. This test consisted of a series of stations where students conducted a short activity that was presented to them. Over 1000 students from 32 Ohio schools formed the sample for this study. Data are presented by skill and by task. In addition, analysis for gender and school effects is included.