Candygram!
Use an index card or piece of cardstock/cardboard, with different candies conveying your special message...

• I appreciate all the Nuggets (Hershey's Nuggets) of knowledge you share!
  
• You make me Snicker — thanks for the laughs!
  
• Sending Mounds of support!
  
• You have so many great Twix up your sleeve!
  
• You're putting in a Whopper of an effort at school — I'm proud of you!
  
• I love you is the Reese's-son for this card!