What are some reinforcing consequences you can deliver either immediately following the desired behavior or following a practice session– things that this particular student enjoys, wants, seeks out, etc.?
Are you using labeling and social praise to make the contingency between desired behavior and reinforcing consequence clear to the student?
As the student learns to seek clarification when she suspects sarcasm is being used, social praise can be really reinforcing. Some students may be uncomfortable saying “I don’t understand” or asking for clarification, and rightfully so since it requires quite a bit of confidence. When she does ask for clarification in scripted role-plays or natural opportunities in the classroom, be sure to state your appreciation of her seeking clarification and clearly label why (e.g. “Thanks for asking what I meant by that phrase. ‘Throwing the baby out with the bath water’ sounds mean, huh? What I meant was…”).
What reinforcing consequences can you arrange that are more naturally or intrinsically connected to this targeted behavior?
In situations where the student expresses or identifies idioms or sarcasm in a friendly manner, reinforce success with the natural consequence: laughter!