There have been multiple calls to incorporate the teaching of scientific practices within science laboratory courses over the past decade. To accomplish this goal, changes must be made to the curriculum standards, instructional programs, and assessment-evaluation systems used in laboratory courses. One instructional program that can used in a laboratory course to help students learn scientific practices such as investigation design, collecting and analyzing data, argument generation and critique, and science writing is the argument-driven inquiry (ADI) instructional model. This article describes the development of an end-of-course assessment, the Investigation Design, Explanation, and Argument Assessment for General Chemistry I Laboratory (IDEAA-GC1), that educators can use to measure students' ability to use scientific practices after incorporating the ADI instructional model into the General Chemistry I Laboratory. This new instrument has strong face and content validity as well as consistent instructor grading. The face validity of the instrument was established through iterative revisions of the IDEAA-GC1 based on faculty and student feedback. Content validity was established through the alignment of the IDEAA-GC1 with scientific practices and anchoring concepts as described by the Three-Dimensional Learning Assessment Protocol and the General Chemistry Anchoring Concepts Content Map.