Yes, though there are limits in Maryland.  Remember that anyone being questioned any time, anywhere by police has the right to remain silent.

No specific rules place limits on police coming into D.C. schools to question students.   

Maryland limits police questioning of students at school.  Police can’t question you at school unless they’re investigating a crime that occurred at school or unless waiting would compromise the investigation or endanger students or staff at school.  A school staff person has to be present throughout and the school must promptly tell parents about the police questioning of the student.  And police can’t take a student away from school for questioning without a parent’s consent. [1]

[1] COMAR § 13A.08.01.13 (detailed rule concerning police questioning students at school).