Should a left handed kid starting out always be taught to fight southpaw?

[greynotsoold]

There is a huge advantage to having the hand you are most comfortable in using being your lead hand: It does 80% of the offensive work, while your rear hand primarily defends.

I think thats very true. Bruce Lees Jeet Kune Do utilized that right at the beginning it was the first way round you'd learn. Same in Wing Chun they taught you how to strengthen your weaker side first. But both these styles switch stance as they fight by style.

Do boxing trainers make beginners use their strongest hand out front very often?

Generally, no, I don't think so. In most cases I think it would be a left handed guy fighting orthodox (like Cooney, or Basilio) though Michael Moorer was naturally right handed.
I read about a trainer in New York, late 80s or very early 90s, that had a real run of success in the Gold Gloves tournament. He turned everybody southpaw, unless they were left handed. They boxed orthodox.