A change in the penalty for illegally equipped players was one of three rules revisions approved by the National Federation of State High School Associations (NFHS) Soccer Rules Committee at its annual meeting January 27-28 in Indianapolis. The rules changes were subsequently approved by the NFHS Board of Directors.
The first caution (yellow card) for an illegally equipped player is issued to the coach, a rule that was implemented last year.

So, yes, a coach can be carded in high school.

"Boys, even if it means dying on the pitch, we must win!" Marc-Vivien Foe 1975 - 2003