In the David Reimer case, how would you redesign the study so it meets ethical guidelines?

There's no way to do ethical human experiments on children.

But for starters there are a million confounding factors and no monitoring of what he had been told about himself or believed.

I'm not sure it could EVER have met ethical guidelines, but the first thing I'd do is make sure John Money wasn't involved.

At all.

Reimer should never have been raised as a girl. If he hadn't been, no "study" would have been conducted at all.

I am familiar with the case. David Reimer was the victim of a botched circumcision that caused his penis to be cut off. His parents then took him to a doctor who recommended that the rest of his sexual organs be removed and he be raised as a girl. The problem was that he didn't identify as being a girl and it caused him all kinds of problems. A better solution would have been to leave him the way he was until medical science improved enough to be able to reconstruct his penis and he could have grown up as a man instead as what he termed as being an "it".