Getting to your placement city

Intercity Transportation within France

Most people I assume will be flying into either Paris Charles De Gaulle or Paris Orly airport. No matter what form of transportation you take afterwards, ensure you have enough time to make the transfer. If you fly directly to Paris from the US or UK you'll have to go through border control. That plus picking up your luggage can easily take 1.5 hours. Planes are often delayed so I would budget another 1 hour. In addition, taking a train, bus, or taxi from the airport to a Paris train station may take over an hour.

Therefore, as a good rule of thumb I would suggest a Minimum of
- 3 hours between scheduled plane arrival and train departure directly from CDG airport
- 4 hours if traveling from a station elsewhere in Paris.

Even with these minimums you aren't guaranteed to make your connection. Maybe your flight will be delayed by 2 hours so plan for whatever your risk tolerance is.

From the airports you have 4 main options to get to your placement city.

1. Train

- Taking a train is usually the most efficient means of intercity transport in France. There are a confusing number of different train systems:

Types of Long Distance Trains

For most of the long distance trains you'll need a reservation in advance. Tickets for all national services are available at www.sncf.com/en and are usually available for purchase about 3 months in advance or 6 months for OuiGo service. Ticket prices tend to only go up over time so it is best to book your tickets as soon as you can. 

- TGV (InOui)

High speed "bullet" train service.

- OuiGo

Low cost TGV service. Same type of trains. Tickets can only be bought online at the same SNCF website as regular TGV.  Extra fees for Baggage. No cafe car. Sometimes use less convenient stations, travel at odd hours, etc. No youth discounts.

- Intercités

Long distance trains, but much slower than TGV. If you book in advance, TGV trains are often faster and cheaper, but last minute tickets may be cheaper on Intercités. Many medium sized cities will not have any TGV service, but will have direct Intercités from Paris.

- Intercités de Nuit

Intercités trains, but with bunk-bed sleeper cars. They used to be more common, but with widespread TGV service, budget cuts, and EU laws regarding rail fees these trains are dying out. However, if you are going to cities in the South of France such as Toulouse or Nice, these are an interesting option.

TER

TER trains act more like metro trains, making more stops than other trains. They have a fixed ticket price, no reserved seats, and cannot sell out so no need to buy in advance. In many smaller cities in France, they are the only rail service available. Each region runs TER slightly differently regarding youth and other discounts.

Cross-Boarder Services

For international trains connecting France to other countries you have: 

Eurostar to London, Thalys to Belgium and Netherlands, Thello to Italy, TGV Lyria to Switzerland, and  ICE to Germany.

Discount Options

- Carte Avantage Jeune

Available to those age 27 or younger, the Carte Jeune gives you 30% off almost all TGV (InOui) and Intercité trains and some TER trains for 49€ per year. If you plan to travel regularly, this card will pay for itself. You can buy the youth fares online and then buy your youth card at kiosks once you arrive at the train station. You will need a passport sized photo to tape to the card. SNCF regularly offers this card for half off on black Friday.

- TGVmax

Another option for those age 27 or younger, TGVmax is a subscription for unlimited TGV and Intercités travel for 79€ per month. You must subscribe for a minimum of 3 months. The problem and the reason I would not currently recommend TGVmax is that there are a limited number of tickets allocated for this subscription. Even if you attempt to book tickets the maximum of 30 days in advance, trains may already be sold out, and this is likely to be worse on school breaks and weekends when everyone is trying to travel. Currently you can check to see availability on their website here. 

-Monthly pass
If you decide to live in a separate city from your schools, you can generally buy a monthly pass for transportation to/from wherever you want to go. Your school will also reimburse you half the cost of this monthly pass.

2. Plane

Unless you are teaching in Corsica, I do not recommend booking a separate ticket to fly from Paris to your destination. Trains overall are more frequent, less likely to be subject to delays, and don't require going through airport security once again. However, in some cases it may be worth flying. There are flights to many places in France for $50-70.

Air France / Hop! also offers a one year 49€ youth card, but only for those aged 24 or younger (if you buy a card at age 24 it will no longer be valid on your 25th birthday). The card gives you access to discounted youth tickets which include a free checked bag and the tickets are refundable with a somewhat low fee. Unfortunately not all routes offer youth tickets. As with the SNCF card, you can buy youth tickets online and then buy the card in person at the airport.

3. Bus

-Believe it or not, long-distance intercity bus service was illegal in France until 2015, but now there are many bus companies offering cheap, long distance bus fares. Buses are often the cheapest transportation to cities without OuiGo service, and some buses leave directly from the airport. However, journeys that take 3 hours by TGV may take 9 or 10 hours by bus.
Some Bus companies are:
BlaBlaBus
ALSA
Flixbus
Isilines
Eurolines
You can search for bus routes on a website like comparabus.com, busbud.com, or elsewhere.

4. Blablacar

Blablacar is a ridesharing service, but not like Uber. On Blablacar drivers post long-distance trips that they are planning on taking and then you can request to join them for part or all of the journey. Because of this system, you never know what will be available and many trips might not be posted until one or two weeks beforehand. 

Blablacar also recently purchased the Ouibus network so you may also see results for their buses on their website.

5. Getting to the Bus/train station or Transfering airports.

- Paris Métro / RER
The Métro is pretty self explanatory. The RER is basically an express métro. It makes fewer stops and travels longer distances.

CDG airport has an RER B station in terminal 2.
Paris Orly has the Orlyval train from which you can transfer to the RER B.

If you only have carry-on luggage then the RER B is likely to be the cheapest and fastest way to any train station in Paris. Costs will be around 10-12€. With more luggage the RER could be a bit of a hassle.

- Taxi

Taxis from CDG airport to anywhere in Paris charge a fixed fare of 50€ or 55€. If you manage to travel with other assistants and split the fare, this could be a decent option.

-Bus 

 LeBusDirect offers direct buses between airports and to certain train stations.

Line 3: 22€ between CDG airport and Paris Orly airport

Line 4: 18€ from CDG to Gare de Montparnasse or Gare de Lyon. 

To other stations there may be buses although I myself am not aware of them.

OrlyBus runs from Paris Orly airport to Denfert Rochereau which located somewhat near Montparnasse station.