Prior findings highlight school students' low motivation to study science, while 21st-century education aims to achieve their key competencies: scientific literacy and autonomous problem-solving to be prepared for smooth adaption to quickly changing circumstances. Real-life learning scenarios can meet these shortfalls to engage the learners by the knowledge-in-use perspective. This, however, requires that learners have high-level abilities of complex learning. We conducted a case study of outdoor learning with 8th-graders (age 14-15) to foster their scientific thinking addressing a real-life problem hands-on. Although the results showed that students' conceptual knowledge increased, they also indicate participants' cognitive taxonomy difficulties. An insight into the cognitive load aspects is given as it may appear in different autonomous learning situations. This work highlights the aspects little discussed so far (1) school students' varying cognitive skills; (2) difficulties arising from the high cognitive load caused by multitasking, accompanied by the complex learning approach. This raises the questions of how to conduct motivating science lessons, where to practice the multi-component learning skills; and how to foster autonomous learning, where to gain the relevant knowledge without overburdening novice learners.