I used joyceisachoice's Valentine's activity for my ES and JH classes this year, and I made some modifications based on what my needs were and what I noticed students struggling with. The ES activity is a modified version of joyceisachoice's letter writing activity, while the JH activity is original.
The vocabulary will likely be new to ES 3rd and 4rd graders, but ES 5th, 6th, and JH students should have been exposed to most of these adjectives before. My ES 5th to JH schoolers were also able to reference their picture dictionaries or the reference pages in the back of their textbooks for additional adjectives.
All levels start with a general 5 minute PowerPoint presentation about Valentine's day in America, which then leads into an activity where students write a letter to their classmates.
At Elementary School Level (and JH Year 1)
Students will be writing down adjectives that describe their classmates.
Students will begin by writing their own name on the line inside the heart. If they can, they should write it in English, though if they are still not very good at reading English words (such as 3rd and 4th graders), I also recommend them write their name in Japanese to make things easier during the next step.
Next, have each student trade papers with their partner.
Explain what "you are" means to the students, and tell them to think about what kind of person is the person whose paper they have.
Review adjectives that the student can write, then ask them to write that adjective down. (example: "OO-san is amazing", have them write "amazing")
Make sure everyone has written at least one adjective, then have everyone trade again with a new person, and have that student also write an adjective describing the student whose name is inside the heart. Repeat until enough time has passed or everyone has written on everyone else's paper, whichever happens first. By the second person, most students understand what they are supposed to do and will start running around trading on their own.
Notes for ES: joyceisachoice recommended collecting all the cards and checking to make sure they were appropriate (and adding additional adjectives to pages which didn't have enough), then handing them back during the next class period. I personally competed this activity and had everyone get their pages back in a single class period. My class sizes are small and my students are generally well behaved, so do what works for your situation.
*The difference between the ES and JH 1Y presentations is how much Kanji is in the PowerPoint. I found that ES students struggled with the kanji on the last slide.
JH Level:
Students will be writing a small, simple poem to their classmates based on the "roses are red" poem.
Begin by giving all the students a secret partner. Hand out class numbers or names written on a piece of paper to everyone. Then have all the students write their partner's name on the line inside the heart.
Next, review the Poem "roses are red" from the PowerPoint. Tell the students that they are going to keep everything the same as the original poem, except for the third line ("Honey is sweet"), which they are going to change and make their own.
Tell students to pick an adjective which describes the student. Then tell them to think about something else which that adjective also describes. Have them fill in the words they have chosen into the poem. (example "Hockey is cool"; "Dogs are cute") *You're gong to get some very interesting poems here.
Make sure they sign their own name at the bottom.
For both activities, if there is time left over (or if some students finish early while others are still writing) tell them that they can decorate and color-in the line art on the letter. Let them flex their creativity.