This study examined the effects of metacognitive scaffolds on learning outcomes of collaborating students in an innovative learning arrangement. The triads were supported by computerized scaffolds, which were dynamically integrated into the learning process and took a structuring or problematizing form. In an experimental design the two experimental groups receiving scaffolds were compared with a control group. The experimental groups differed in the form of scaffolding used: structuring scaffolds versus problematizing scaffolds. We analyzed the effects of metacognitive scaffolding and of different forms of scaffolds on the learning outcomes at group and individual level. The results showed no effect of scaffolding on group performance, nor on the acquired individual domain knowledge, but a small effect on acquired individual metacognitive knowledge. With respect to the effects of different forms of scaffolds, we found a small effect on group performance, on transfer of individual domain knowledge and on the individual metacognitive knowledge acquired. (Contains 5 tables and 3 figures.)