What is constructivism in simple terms

Similarities of Behaviorism Constructivism is similar to cognitivism because they both focus on meanings.
Constructivism is based on interacting with the knowledge to develop meaning for it.
Cognitivism is a theory that focuses on presenting information in a clear way so that students can have a better meaning of it.

In my opinion the worst thing about constructivism is that it is espoused as a goal for all students and teachers but in reality classes are judged upon their performance on state exams.
For example, my colleague had students build model roller coasters in her physics class.