You can do your training with any qualified motorcycle riding instructor. All approved CBTA assessors are qualified motorcycle instructors and are able to tailor training programmes to suit the stage of riding you're currently at.
There are also government-subsidised and tailored training courses available through the Ride Forever National Training Programme. Ride Forever courses provide extensive on-road training. The core competencies covered are based on the skills required for the assessments. The courses are available throughout New Zealand. Visit the Ride Forever website at www.rideforever.co.nz/training for more information.
You can start training for either stage at any time after getting your learner or restricted licence, so you're fully prepared to undertake the assessment. Once you're satisfied that you're competent in the skills required for the assessment, you can book and undertake the assessment ride.