Is there a legal defense for this that parents can use?
Yes there is
Taken directly from the IDEA regs
(25) Prohibition on mandatory medication.-- (A) In general.--The State educational agency shall prohibit State and local educational agency personnel from requiring a child to obtain a prescription for a substance covered by the Controlled Substances Act (21 U.S.C. 801 et seq.) as a condition of attending school, receiving an evaluation under subsection (a) or (c) of section 614, or receiving services under this title.
(B) Rule of construction.--Nothing in subparagraph (A) shall be construed to create a Federal prohibition against teachers and other school personnel consulting or sharing classroom-based observations with parents or guardians regarding a student's academic and functional performance, or behavior in the classroom or school, or regarding the need for evaluation for special education or related services under paragraph (3).
Here is the link for verification -
http://idea.ed.gov/explore/view/p/%2Croot%2Cstatute%2CI%2CB%2C612%2Ca%2C25%2C
Any questions? -