probably in the area of 4 to 6 - Instructor needs to make sure student is executing in flawlessly. My first go-around happened before I was trained to do go-arounds - guy on a flexi wing had a wind gust knock him off runway - I applied full power but kept the nose down to rubber neck and see if he's all right. My FI wasn't impressed, but sure enough once you can demonstrate that you understand the concept a couple of consecutive times you're good to go