Tips for tasks assessing a candidate's OO PHP capability

I recently interviewed a candidate for a web developer position who seemed OK, but admitted that his previous role hadn’t exposed him to much object orientated PHP.

Normally when I give candidates technical tests I give them fairly simple tasks to assess the cleanliness, logic and security-conciousness of their code, but this time I’d like to specifically test how well he does with some intermediate object orientated tasks.

Any suggestions as to what kind of task to give?

What do you consider to be an “intermediate object orientated task”?

I’d be scared based on the “hadn’t exposed him to much object orientated PHP” comment. I’m not sure what the exact specifications of the job are and I don’t want to be the one to prevent someone from getting a job. But at this point not being exposed to and very comfortable with OOP at a minimum and ORM’s, MVC, design patterns, etc, would probably be a disqualifier unless you only require the absolutely most basic procedural PHP programming or this candidate has extensive experience in some off-required specialty. I would consider all of these to be fairly run of the mill programming nowadays.