rich r wrote:there is no reason someone shouldn't be able to start to stand in whitewater - longboard or shortboard.
If you can't, then you are missing out on another critical aspect - paddling for the wave.
Practicing in the whitewater can help you learn that 'feeling' of when you're getting picked up by the wave, and thus the right time to pop up. It also demands a bit more of a paddle, and learning timing by watching when the foam is approaching, etc..
All things that translate into moving out to the shoulder and then eventually into the lineup near the peak.
This varies by locale - where I surf, the breaks usually don't push very far. There is an outer sandbar, and if you try to stand up in white water you've often got about 2 seconds to do so before the white water ends and the wave calms and its not rideable again until it re-breaks on shore way inside. 2 seconds wasn't enough for me. So finally I ignored this advice, and went out and learned to get waves in the green, just before they broke. Only THEN was I able to learn the pop-up.
So this varies. Its not universal that its best to catch whitewater first until you get the pop-up. Some places don't have good whitewater. The whitewater was good for about two days of practice. After that I needed to be out catching them just before they broke. I think its that way everywhere in Florida.