A former teacher’s aide at Maynard High School pleaded not guilty in Concord District Court on Tuesday to charges of providing alcohol and marijuana to minors, Middlesex District Attorney Gerard T. Leone Jr. said. Jennifer Olsen, 41, of Maynard, was charged with four counts of procuring alcohol for a minor and two counts of a drug violation in a school zone, among other charges, Leone’s office said. In two incidents last month, Olsen allegedly smoked marijuana with four high school students, Leone’s office said in a statement. The school terminated Olsen on Nov. 5, the statement said. Olsen was released on $1,000 bail, Leone’s office said.