Even though clapping may seem more useful for younger students it may work in the classroom because it causes the students to pay attention to the variation. You may also consider pulling objects that will be used throughout the class period and placing them up front so as students come in they see these and will be curious as to what's going to happen. If they don't respond, shutting the lights on and off may grab their attention enough to get them quiet so you can start with your attention getter.

Science is a great subject for hands on exploration. Start your lesson with an attention grabber (hook) that will get the students attention without speaking. Once one student start looking and paying attention the rest will follow. Keep the students engaged by having them do activities that require them to collaborate and use the students energy in your favor. Create stations around the room so the students have to move around. Make the stations collaborative so they are still able to talk, but it is about science.

I would try implementing a strategy of your own to the students. Maybe something as simple as saying, "if you can hear my voice clap once, if you can hear my voice clap twice." Just because the classroom teacher yells to resolve her problems, does not mean you have to.

Whether you are aware or not, your body language says a lot about you. Stand with confidence. Have a "Do Now" on the board when they enter the class so there is no time down time. Find the ringleader and hold him accountable for his behavior by enforcing the school and class rules on him. You can also start the day by reviewing the class rules and inform the class that you will be enforcing them and there will be consequences for breaking them- AND FOLLOW THROUGH!

I have a bell on my desk that I ring to bring the students back to attention. When the students hear treble they know I mean business and they refocus.

If you feel that yelling doesn't help get their attention, try different strategies. Talk to other teachers of other subjects and see what works for them. Sometimes clapping or a simple 'if you can hear my voice, clap once' helps get their attention back.

It might not be a useful strategy but you must remember that it is their classroom not yours. You are in the class because you need to be there not because the teacher needs you. Handle yourself and situations you come across professionally but i would be hesitant with how you approach that teacher especially if you were planning on saying something to that person. Take this experience and learn from it more than anything else. Dont make the same mistakes when you get your own classroom!

Identify the problem student(s). Bring them to the side and ask probing questions as to why they are being disruptive and explain to them how they are leading the other students to copy their actions. Let it be a friendly warning... Try that out.