None of these solutions worked in my case but here is what did....
The situation was a header that was divided into 3 components (Pages uses 3 components by default). The left had a logo that was un-selectable. The right had some right-aligned text. The middle had some returns and a horizontal rule that ran across the bottom of all three components.
The middle component had stretched the header container (with all 3 components) to cover the logo so that clicking got the empty left container -- as a background image, Pages had put the logo behind the left container rather than leave it in it. Using the "drag a marque starting in the grey off-page area" didn't work to select the logo.
Deleting some of the returns in the middle component -- which shortened the height of the header overall -- exposed enough of the bottom of the logo that it was now selectable.
I hope this helps someone.
And to join the chorus, Pages (and Numbers) aren't up to the quality standards I expect from Apple. I'd happily pay Apple for Pages if it meant that the program was better. As it is, I can't currently recommend it for either business or school use.