Our research objectives focused on monitoring (i) students' activities during experimental teaching phases in an out-of-school gene technology laboratory, and (ii) potential relationships with variables such as work group size and cognitive achievement. Altogether, we videotaped 20 work groups of A-level 12th graders (n = 67) by continuous recording of their laboratory-work phases. Subsequent analysis revealed nine categories characterizing the students' most relevant activities. Intra-observer and inter-observer objectivity as well as reliability scores confirmed the good fit of this categorization. Based on the individual time budgets generated, we extracted four clusters derived from students' prevalent activities. A cross-tabulation of two cluster analysis methods independently used showed a high level of agreement. Clusters were labelled as (i) "all-rounders" (members of which applied similar portions of time to the main activities), (ii) "observers" (members dominating activity focused on in-group observation of the laboratory work), (iii) "high-experimenters" (members predominantly engaged in specific hands-on activities), and (iv) "passive students" (members mainly engaged in activities with no experimental relation). Particularly, we found members of Clusters 1 and 2 in four-person work groups while members of Clusters 3 and 4 were prevalent in three-person groups. During the educational intervention, students of all clusters improved their cognitive achievement on a short-term and a long-term schedule. However, only the "all-rounders" revealed a high level of persistent (long-term) knowledge with no decrease rate at all. We draw conclusions with respect to work group sizes as well as to organizational aspects of experimental lessons. (Contains 5 figures and 5 tables.)