The other night, DD was doing prealgebra homework (writing down equations for an arithmetic series). She could do the increasing ones, but couldn't immediately figure out how to write an equation for the decreasing ones. The entirety of my help was to ask, "OK, so this one is correct - explain to me how you got that answer. How do you know what this coefficient is? Now, what do you think you could do to apply the same rule to solve this one?" Then I bit my tongue for a full minute while she stared at it. Then she figured it out and banged out the rest of the assignment.
I see that as an appropriate level of parent help.
I have typed answers at her dictation for online forms (e.g., camp enrollment questions), but I don't think I've done one for a class assignment since first grade, and I got teacher permission ahead of time for that.