Possible Clues:

• School tie?
• Gp. that supports summer reading
• School gp. that sometimes has an 'S' added to its name
• School grp. for adults
• Niña accompanier
• Grp. involved in back-to-school night
• "Harper Valley ___" (hit of 1968)
• Booster gp. for schools
• National grp. since 1897 that elected its first male head in 2009
• Harper Valley letters