The federal courts have routinely held that schools can prohibit students from using the restroom during class time when the student misses instruction. See Tinker v. Des Moines Independent Community School District, 393 U.S. 503 (1969); Jackson v. Dorrier, 424 F.3d 439 (6th Cir. 2005); Doe v. Pulaski County Special School District, 306 F.3d 539 (8th Cir. 2002); Thomas v. Roberts, 223 F.3d 575 (7th Cir. 2000); Horn by Parks v. Currituck County School System, 267 F. Supp. 2d 493 (E.D.N.C. 2003); and Rucker by McCoy v. Haupt, 94 F. Supp. 2d 847 (E.D. Mich. 2000).
Additionally, public schools are required under the Americans with Disabilities Act, 42 U.S.C. §12111(8), to provide disabled students with restroom breaks when needed.