I just found this blog and it seems both very interesting and very useful for IB Economics students so I decided to let you know about it and upload the link for all of you. It was originally uploaded by a colleague (Patricia Hermes) on the OCC, the site for IB economics teachers (thanks Patricia!).
The externality analysis on helium ballon consumption is very close to what I consider the appropriate framework (check out the diagram used) and skimming through other posts makes me quite confident that many of you will bookmark the link for future regular reference.
This is the link (I will also add it on the RHS of this blog).