How to take the rail journey from Madrid to Tarragona

The high speed line between Mardrid was built to the north of Tarragona, so Camp de Tarragona station is 11km from Tarragona city centre.
However, there is a bus connection to the city, though the buses seemingly aren't co-ordinated with the train arrivals from Madrid, so you may be waiting up to 50 mins for a bus to depart.

Final Destination: Barcelona or Figueres or Marseille
If you depart Madrid at 13:25 you'll be travelling by the AVE 100 train, which will be heading to Marseille.

Noe that the iryo and Ouigo services which also use the Madrid to Barcelona high speed line, don't call at Camp de Tarragona station.

Book early and save: Yes

Online bookings open: up to 6 months ahead of the travel date - depending on the time of year.

The online booking window can be shorter between late July and early October.
When looking up journeys (not travelling) between late July and early October, it's likely you won't be able to book for journeys beyond the second Sunday in December.

Spanish national rail operator Renfe doesn't operate a 'Ticket Price From... €x' on this route, prices are set according to demand per departure - hence the lack of price info below.
The slower trains can be cheaper, as there is inevitably higher demand for the faster trains.

Difference in core ticketing terms between AVE and avlo services:

Child tickets:
avlo = children aged 13 and under travel for a flat rate of €5, maximum of 2 children per fare paying Adult.
AVE = children aged 5 -13 and under are entitled to a 40% discount.
If you want to place a child aged four and under in its own seat, they will also have a 40% discount on the ticket price, but if you'll be happy to travel with the child on their lap, then there is no charge.

Amending booked tickets
avlo = pay an additional €8 when making the initial booking and you can then make one change to an alternative choice of departure.
AVE = promo + ticket holders will receive 80% of the ticket price refunded if you then want to book a different service, but you will then have to re-purchase a new ticket for the train you now want to take

Seat Reservations:

Seats will automatically be assigned when booking tickets for this journey.

Rail Pass Users:

Spanish national rail operator RENFE does not sell rail pass reservations online, but reservations for journeys on the AVE, Alvia and Euromed trains are now available by using the Eurail reservation service or the InterRail reservation service.

The only option, other than booking them at a station in Spain, is to pre-reserve seats by calling Renfe phone sales: +34 91 232 03 20.

Pre-reserving a seat is possible up to 24 hours before a train's departure. You will receive a PNR code which you must use to pick up and pay for your reservation at a local station ticket office, making sure to show your Interrail Pass. You must collect your reservation within 72 hours. After this time the pre-reservation will expire.
Please note that a pre-reservation is not the same as a reservation. It only holds a seat for you for 72 hours.

A plus of taking this train is that it arrives in Tarragona station in the heart of the city.
In contrast the AVE trains arrive at Camp De Tarragona station, which is 11km north of the city and has bus transfers to central Tarragona.

This train is scheduled to depart from Madrid-Charmartin at 07:15 on Mon-Fri only.

Final Destination: Barcelona Franca

Book early and save: No

Online bookings open: Two weeks ahead

If you haven't booked before your date of travel for an AVE train between Madrid and Tarrgaona and have time on your side, then it's likely that you'll be making a big saving by taking this train.
Though if you can book even a couple of days ahead, it's likely that you'l find cheaper tickets for the AVE trains.

Rail Pass Users:

Reservations aren't available on this Regional Express train, so if you're travelling on a budget and won't mind spending all day on a train, then it's possible to to travel from Madrid to Tarragona without paying any additional fees,   if you'll be travelling with a valid Eurail or InterRail pass.

If you have a 2nd class pass you'll save €10 and if you have a 1st class pass you'll save €23.50; though as this train is 2nd class only, there's quite a contrast between travelling on this train and in Preferente/1st class on the AVE trains.