School lunches can now offer tofu as a "meat alternate," thanks to a little-noticed announcement from the Department of Agriculture in January. If you're looking for it in the government code, it's at "7 C.F.R. 210.10(c)(2)(i)(D) of the regulatory text for the NSLP," so just flip on over to that sub-sub-sub-sub-subsection.
Here's the USDA's announcement.
While tofu does not currently have a Federal standard of identity, the current Dietary Guidelines for Americans (DGA) encourage plant-based sources of protein such as tofu. According to the DGA, consumption of a balanced variety of protein foods can contribute to improved nutrient intake and health benefits.
Not to get post-modern, but who among us does have a federal standard of identity? (You'll soon need one to vote in various Southern states.)