"Can" isn't very hard to explain, and when I taught elementary the kids really enjoyed the lesson. I introduced it about 8-9 months into the year. At this point we had learned some easy verbs like swim, run, walk, jump, fly and climb. This took 35-40 minutes if I remember rightly.
It went like this:
- Practice the action verbs with some kind of gesture game/Simon says.
- Introduce some animals (ideally taught previously or with similar names in Japanese, like penguin, lion, etc). Put their pictures up on the board.
- Put up a poster-sized version of this grid (click to download).
- Go through a few of the animals, saying "This is a penguin. A penguin can swim, but a penguin can't fly." Use gestures/maru and batsu to help translation (no Japanese should be needed). Keep going until they seem to get it. Then ask them "Can an elephant fly?" etc to fill out the remainder of the grid. Just your inflection should be enough for them to get it, you don't need to teach the grammar. You can do all of them if you want/have time.
- Put students into small groups (2~4 students or whatever you want) and give them a completed grid as a regular-sized sheet (or get them to complete it as you do the point above).
- Play the "three hint quiz". Call out three things your chosen animal can/can't do, and they have to shout out which animal it is. If you have time they can then play this with each other/one student infront of the class. You can also bring in things from other lessons, like colours etc as hints.
The Janken Game (10+ minutes)
Great fun game for elementary/low ability. Bigger (over 20 students) classes can be a bit of a strain, and kids at the back of the lines will get bored.
- Make around 10 sheets with a word/picture on each from the target vocab/review (in this case animals),
- Put them up on the board from left to right. For this version, put up a flashcard of one of the verbs,
- Split the class into two groups and line them up either side of the board,
- One student from each group must go along the board shouting out the word from the card/picture and the verb (e.g. a bear can swim, a dog can swim, a bird can't swim),
- When the two students meet in the middle, they janken. The loser goes to the back of his/her group line.
- The next student from the losing group must start again from the beginning.
- The aim is for one student to get all the way across the board. If they do, the team gets one point and they go to the back of the line.
- Keep going until time is up/they're sick of it.