Can't find a document to support, but my last school had it clarified as a passenger could be carried, but had to be part of the lesson, ie "learning by observing".
Generally this works pretty well in practice, either on gift vouchers or taking a friend or family member along on a lesson as a "taster" to see if they wanted to take it up themselves, or even taking two PPL students along for a land away to swap over and save them some money. I also did plenty of back seating during my IR which really helped.