This exploratory study investigated 100 Israeli 9th graders who used two different group-metacognitive support methods in online mathematical inquiry--group feedback guidance (GFG) and self-explanation guidance (SEG)--compared to a control group (CONT). The study evaluated each method's effects on students': (a) mathematical inquiry ability: problem solving, explanations, mathematical feedback in online forum discussions, and transfer ability; and (b) self-regulated learning (SRL) measures (self-report questionnaires and metacognitive feedback in online forum discussions). Metacognitive support methods, based on IMPROVE self-questioning strategies, appeared in pop-up screens and provided the two experimental groups with differential cues for problem-solving processes. Mixed quantitative and qualitative analyses showed that GFG students outperformed SEG students in most mathematical and SRL measures and the CONT students in all measures. In addition, SEG students outperformed the CONT students in mathematical problem-solving but not on mathematical transfer ability or SRL. (Contains 5 tables and 3 figures.)