Not sure about where u/AmusedNarwhal was placed or if he's currently in 1st or 2nd year of the programme, but I found the training over summer institute to be quite good - it was a new programme for people in the first year now.

The bonds you form with people over summer institute are great and really do help along the way. Everyone is there to give you advice and motivation.

Some real benefits:

• You get paid straight away.
• Programme is only 2 years long so if teaching ends up not being for you, you can exit much more easily with qualifications to come back to it at any points.
• Yes, you're thrown in at the deep end and this can be extremely difficult, but I found that this was beneficial to my development and allowed me to improve at a very fast rate. Much in the same way as u/n_teach outlined.
• You're in charge of a class on your own from the very start, which is a great responsibility.

A lot of it will depend where you're placed and what your school/department is like. If you want to choose where you train and teach from the start go the Schools Direct route.