Directions say this?
By default, dragging with the Direct Selection tool 
adjusts multiple related segments, letting you quickly transform path shapes. To edit only segments between selected anchor points, reflecting previous Photoshop versions, select Constrain Path Dragging in the options bar.
I can't find it to save my life. Please help.
Is Window menu > Options checked? Doing that makes the Options bar visible.
If so that option is on the far right of the options bar which should sit below the main menu bar at the top.
I saw that before and yes, it is clicked as you can see in the attached photo. I noticed it go away and come back as I clicked it and of course being labeled Options I was sure that was it. So after that I still don't see the Constrain Path Dragging. In fact mine doesn't look like yours. Mine has an additional choice of Auto Add/Delete which is checked. If I uncheck it nothing changes other than it being unchecked.
Im still stumped. This is a real copy of CS6 purchased. It is the Adobe Creative Suite 6 Design & Web Premium. Allows for 2 computers and so far I am the only one who has installed it.
Anything else?
TADA!!!! So I noticed the tool you were selected on when Constrain Path Dragging was in the options bar. I was on the pen tool so I figure that MUST be where that should be. Apparently I was wrong. I selected the black arrow and Viola! There is was.
Now to play. Thank you thank you thank you. I am sane again.