There were three different types of cards used during the draft, with slight variation in the questioning. One of the cards looked like this one:
This card belongs to Artie Lee Barnwell, who was a first cousin four times removed of mine. (I have images for closer relatives, but this is the largest and most clear one.) I draw your attention to Question #4:
4. Are you (1) a natural-born citizen, (2) a naturalized citizen, (3) an alien, (4) or have you declared your intention (specify which)?
Notice that there are only two categories of citizen: (1) natural-born, and (2) naturalized. That's it. No third category that amounted to 'citizen since birth but not the natural-born variety.' To buy the Birther theory of citizenship is to suggest that a lot of young American men had no applicable box to check on this form.
The interpretation of these categories is also straightforward, as it would have been to the people of the time. For example, my great-great grandfather Ingwer Dockweiler, who immigrated from Germany and subsequently went through the naturalization process, was a 'naturalized' citizen. His son, Fred, who was born in North Dakota, was a 'natural-born' citizen, simply by virtue of being born in North Dakota.
The other two types of draft cards used different language for this question, but serve to bolster this straightforward duality of citizenship. One type of card had five boxes that one could check, three under the heading of 'U.S. Citizen' and two under the heading of 'Alien.'
The three 'Citizen' box options were "Native born," "Naturalized," or "Citizen by father's Naturalization before registrant's majority." The two 'Alien' options were "Declarant" or "Non-Declarant."
The third card had these options:
Native of the United States
So not only did the U.S. Government not have a third category for 'Born in the U.S. but not a natural-born citizen,' but it considered "Natural-born citizen" to be effectively synonymous with "Native born citizen" and with "Native of the United States."
Now I'd love to close out this post with an image or two of young men born in the U.S. to aliens stating on their forms that they were "Natural born citizens." Unfortunately, my own family immigrated long before the 20th century, and I only have images handy for my own family. However, I do have research access. So I'll end with a request.
If you had ancestors who immigrated around 1900 and had a son soon thereafter, a son who would've been draft age in 1917, let me know. I'll pull the draft cards for you, and illustrate that a boy born of aliens in the United States was a natural-born citizen.