Head size / shape is a sure fire way for failure! So is phemoral pores. Lifting the tail & checking for the bulges is the best bet.
At 6 weeks for the most part, if it looks like a male, then it most likely is. Females on the other hand, my not be as they look. Some males can take a little longer to develop their "stuff" so a 6 week female may with time, turn into a male. (not literally, but with the reason above)
The best way to check young dragons is to lift the tail & kind of rotate it in your fingers. Kind of like holding a pencil by it's eraser, & the point is pointing down, then roll your fingers so it goes right to left. (I hope that makes sense).
That helps put some pressure on male genitals and helps them show. If they are in shed in that area, it's very hard to tell even with the rolling of the tail.
Good luck.
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Joel R
Coming some day.
www.SpikesAndScales.com