The assessment of students’ manipulation skills is often neglected by teachers. This trend can be partially attributed to traditional assessment practices which focus upon what the student writes in a lab report rather than the student’s physical performance during the lab activity. Therefore, this article reports on the processes which were undertaken when designing the Performance-Based Lab Assessment Technique (PBLAT). The PBLAT can be used to assess the process skill of manipulation of equipment/materials in biology (i.e. assembling, measuring, and experimenting) as the students conduct science lab activities in high schools and colleges/universities. The PBLAT is not limited to biology lab situations as it can be adapted to other sciences.