I don't teach that level myself to have anything tried and proven but this website is always good for ideas.
http://genkienglish.net/juniorhigh.htm
There's a game listed here called Criss Cross
1. All the students stand up.
2. Ask a question.
3. The student that wants to answer raises their hand.
4. If they get the question right then all the kids in their row of desks (ie. all kids to the left and right of them) sits down.
5. Ask a question. The student that wants to answer raises their hand.
6. This time if they get it correct all the students in the column they are in (all the kids in front and behind them) sit down.
7. Repeat from 2 until only one kid is left standing
If the kids are too keen and everyone wants to answer (or in Junior High none of them wants to answer!!), then a good way to choose who answers the questions is to use the Ball and Music Game (see website)
Hope this is of some help. The site is worth a look.
xx jen