I'm interpreting "Teaching language" to be the first language students learn. How can one explain the need for monadic IO properly without explaining how regular printf and the like work. Also, Haskell is quite scary to the beginner (Although I personally find it much simpler/more consistent than the Java and C++)

If it's (say) the third language they learn, then Haskell is absolutely perfect for the exact reason/s you have stated. Personally, I actually learnt Haskell by accident (Read SPJ's book about lazy functional language implementation, realized SPJ started Haskell then learnt more from there).