I have read in many and varied sources that "schoolboy" is street-talk for codeine. Now, somewhere or sometime perhaps it is or was, but not ONCE, as in never, during my reasonably extensive research regarding various street scenes did I ever hear it used. T3s, T4s, codeine...yeah, those one might hear...but schoolboy? Me not think so, unless it is just something pre-1960s and fell out of use.
Dude, I just scored a scrip for T4s 'cause I told the doc my BACK hurt!
(One would NEVER say that one just scored some "school boy.")