Taxis are very safe in, most of the drivers use to be ex-police and have to pass a test on every single street in London before they get their license.  They also won't drive you in circles (like a New York cab would) b/c they would lose their license, which is a privilege.

The subway is the Tube and the card you will get to ride it is called an Oyster. Avoid the circle and district line (yellow/green) whenever possible it is the slowest and most unreliable.

No one knows what a "cell" phone is, they are called mobiles (mo-by-als)

Queue is used in place of line… "we queued up" "the queue starts here"

You say toilet not bathroom or restroom

www.ryanair.com has very cheap tickets, and it is usually better to get a one way on one airline with a special and home on another.

There is a difference between a bus and a coach.  A "bus" is the city buses and a "coach" is what we would consider a luxury bus used on school trips out of town (like to DC in Junior High).  I am mentioning this, b/c you will probably take coaches to go around England with your school.  If you get lost and don't know where the coach parked and ask for the buses… people will send you to a bus stop, not the coach park.

Camden Market is a great artistic place to go find all things ethnic

If you are planning on going on the London Eye (the big wheel on the river) you can get a two for one special with your Oyster.  Also, go right before sunset, so you can see it during the light and can also see the lights at night.  Or you can just go twice

Most places still have two faucets (hot/cold).  You either learn to wash your face with cold water or get a handful of cold and then move it over to the hot.

www.hostelworld.com is a great website to book hostels ahead of time.   

Hyde park is great and on Sundays there is something called Speakers' Corner where people go to rant about whatever they want… god, government, their spouse.  It's awesome.

There is also a mini marathon sometime in October through Hyde Park, I would look when you get there

Things they don't have that you might miss: JIF (they have natural peanut butter), Mac and Cheese, Cheese-its, Lucky charms, Mexican food (including chips and salsa), basically anything over processed or sugar added in large quantities

I did the Hagis/ shamrocker tours in Scotland and Ireland- well worth it. www.radicaltravel.com