Ooh well I could pretend that I'm already the seasoned expert but I've only been working a few weeks...you do learn fast however. Anyway here's my breakdown of the different grades in my Japanese elementary school. Important to know as you don't want to kick off a 6th grade lesson singing the ABC song...
6th graders, 11 years old and going through that "I don't want to be embarassed in front of my friends" stage so can be tricky but they are a sweet bunch, just takes more time to get them going. Don't expect them to clap or jump up and copy your gestures. However incorporate it into a game and they will. Introduce a scoring system and you'll have them do anything! I created a face race track on the board last week giving each team a name according to their mode of transport (a rickshaw, a funny looking bus, a racing car etc) They got soo competitive with the game and got so into it I think they almost forgot they were practicing English language!
5th graders, 9-10 yrs, similar to the 6th graders but a teeny bit more genki (you might be able to get a 5th grader to clap for example but forget it with a 6th grader)
4th graders, 8-9 yrs, cuter, a bit more genki, will definately clap and sing.
3rd graders, 8 yrs, soo cute, play a song and they'll be up standing on the chairs going wild. The kids went crazy during my ball game (hot potato) with an inflatable ball (just make sure you use an inflatable)
I've just had a class of 2nd graders this week (7 yrs) Oh so genky. I wanted to smuggle some of them home they were that cute!