The paper reports a quasi-experimental study comparing the "traditional flipped classroom" pedagogical design with the "productive failure" (Kapur, 2016) pedagogical design in the flipped classroom for a 2-week curricular unit on polynomials in a Hong Kong Secondary school. Different from the flipped classroom where students are provided video clips with new concepts and associated procedures to review at home before solving problems in class, the "productive failure" pedagogical design in the flipped classroom worked the other way around. Supported by mobile technologies, students explored, discussed and solved problems related to the new concepts first in class even though they might come across failures, followed by consolidating the concepts and associated procedures using video clips at home. The pedagogical design is referred to as "productive failure-based flipped classroom" in this study. The study was carried out in two Grade 7 classes: one with "traditional flipped classroom" and one with the "productive failure-based flipped classroom". Findings show that both classes had significant improvement in procedural knowledge. However, regarding conceptual knowledge, students in the "productive failure" condition performed better than those in traditional flipped classroom. This suggests that the "productive failure-based flipped classroom" pedagogical design may be better able to improve students' problem solving skills.