Obviously constructivism is the best way for student to approach knowledge.If U can yourself find out your own materials,and you can create your own ways of understanding,or you can acquire information and ideas from other members in group,I'm sure U will master the knowledge more effectively and longer than you just practice what teachers teach you,right?However,constructivism doesn't always work well in any circumtances. Let's think how this method can be applied in a mixed class,huh?How can the lower-level students keep up with the higher-level ones?It's hard for them to self-study and raise their ideas in front of class because they may ashame of their incapability.This causes the discrimination b/w those students and leads to the bad results in studying.That's why teacher will fail in teaching.