Emphasis on improving higher level biology education continues. A new two-step approach to the experimental phases within an outreach gene technology lab, derived from cognitive load theory, is presented. We compared our approach using a quasi-experimental design with the conventional one-step mode. The difference consisted of additional focused discussions combined with students writing down their ideas (step one) prior to starting any experimental procedure (step two). We monitored students' activities during the experimental phases by continuously videotaping 20 work groups within each approach (N = 31). Subsequent classification of students' activities yielded 10 categories (with well-fitting intra- and inter-observer scores with respect to reliability). Based on the students' individual time budgets, we evaluated students' roles during experimentation from their prevalent activities (by independently using two cluster analysis methods). Independently of the approach, two common clusters emerged, which we labeled as "all-rounder" and as "passive students", and two clusters specific to each approach: "observers" as well as "high-experimenters" were identified only within the one-step approach whereas under the two-step conditions "managers" and "scribes" were identified. Potential changes in group-leadership style during experimentation are discussed, and conclusions for optimizing science teaching are drawn.