In the 1995-1996 school year, the district enacted a policy against talking about LGBT issues, called "Prohibition of Alternative Lifestyle Instruction.

[11] Merrimack High School offers a variety of clubs and activities for the students to participate in.

The school has teams for basketball, baseball, bowling, cheerleading, cross country, field hockey, football, golf, gymnastics, ice hockey, lacrosse, soccer, softball, swimming, tennis, track and field, and wrestling.

[13] The MHS videography department is notable for its yearly student-run spoof productions, such as "Matrix High School" and "Star Sports".

STEM activities include FIRST Robotics Competition team,[14] math team, Science Olympiad[13] Student engagement and academic extracurricular activities include Academy of Finance, environmental awareness, financial literacy, games (separate video and non- video games club), Gay-Straight alliance, heath club, Interact club, Merrimack Mentors, Model UN, newspaper, Quiz Bowl, and the National Art Honors Society chapter #2538.