In an effort to overcome deficiencies in teaching molecular biology at school, a workshop in an out-of-school laboratory including only authentic experiments was developed. Evaluation of 337 A-level 12th graders followed a quasi-experimental design, with one hands-on group, two non-experimental control groups (at school/in the laboratory), and one group with no intervention. Their cognitive achievement was monitored by pre-, post-, and retention tests and analyzed for inter-group differences. Test items were differentiated into the "updated prior knowledge" and the "project-oriented" set relating to new knowledge. All intervention groups increased knowledge either as a whole or in relation to the project, whereas updating of prior knowledge was observed only in the laboratory, independently of experimenting. The hands-on group provided a higher learning success as regards knowledge acquisition as a whole, whereas the non-experimental laboratory group was more successful in updating prior knowledge, both groups in comparison with the school group. Nevertheless, the hands-on group's achievement scores dropped more than those of the school group. Learning motivation may have been higher in the laboratory, furthered by the involvement in experiments, as shown by correlation analysis. However, the experimental situation may comply with the cognitive load theory by a substantially higher contribution of extraneous load.