My best math teachers never made us engage formalisations. What they would do is manipulate us into having an arguement, or construct an apparent contradiction.

My best math teachers never made us engage formalisations. What they would do is manipulate us into having an arguement, or construct an apparent contradiction. We then discussed the problem until we all agree (often without the Teacher talking). The inevitable result of this is that everyone learned formalisation: because it makes for really convinving arguements.