The engaging nature of video games has intrigued learning professionals attempting to capture and retain learners' attention. Designing learning interventions that not only capture the learner's attention, but also are designed around the natural cycle of attention will be vital for learning. This paper introduces the temporal attentive observation (TAO) instrument, an instrument developed to assess attentive behavior sequences during serious gameplay. We use an established three-step process for developing observational systems that includes identifying the construct, determining validity, and demonstrating practicality criteria. We conclude that the TAO instrument reliably measures attention behaviors where participants' faces can be recorded during an experiment. Furthermore, we suggest that TAO should be considered as a part of an attention measurement package.