The objective of this project was to develop a valid and reliable multiple choice test of six basic science process skills for students in grades 4 to 8 (ages 8 to 14 years). Seven criteria were outlined for the test: an emphasis on the six most widely used science process skills (observation, inference, prediction, measurement, communication, and classification); a multiple choice, four-option format; an emphasis on use of pictures and drawings to clarify and enhance items; an average test readability below the fourth grade level; test length that permits completion within one class period (45 minutes or less); a wide range of difficulty of items addressing each process skill; and content-free items. The first version of the 36-item Test of Basic Process Skills in Science was validated and administered to 133 fourth-, sixth-, and eighth-grade students to establish test reliability and to compute item difficulty and discrimination indices to aid in test revision. A second version was then administered to 684 students. Results show this version to be a reliable and content-valid test appropriate for use with students in grades 4 through 8. In addition, the item difficulty and discrimination indices for this final version are reasonably good. (JN)