Well, when I did it (If it is what I think you are referring to) It usually involved me going out in the mornings to turn in, feed, and get the lesson horses ready. Then I would go out and scrub water buckets and then help with whatever else needed to be helped with. I would usually get a lesson for every 2 or 3 hours I worked. Eventually, I ended up test-riding horses at auctions, helping with sales, and riding out the quirks of the lesson horses so it was a little bit less menial work, but I still wasnt getting paid in anything but riding. Thats how I think it normally works.
Sometimes though, if you are working under a BNT or traveling, there is shared housing included and showing opportunities.