Here are some Valentine's Day ideas for multiple grades and subjects.... some are simple and require little to no planning or materials, others require a bit more time and supplies....
This link as a great list of ideas!
Math - Estimation
Have a bag or jar of candy, jelly beans or something and have kids estimate the # inside. Have them explain WHY they estimate that number.
Math - Graphing
Have students graph the number of each colour of candy in a pack or jar you bring. Or if you do not have candy, survey the class on their favourite candy or flower (or anything you can tie into Valentine's Day) and graph the results.
Give students a list of vocabulary words related to the holiday and have them write a story or sentences using the words. Alternatively you can do a memory or BINGO game having students create the cards or game boards to play.
English - Poetry
Share some love poems or sonnets with the class and have them write their own using similar patterns or style. This works especially with short and structured styles like Haiku or Cinquian
Honestly, glue, glitter, scissors and construction paper... the end! ha ha!
What other ideas do you have?