Aes Sedai take it very, very slowly. It seems common for sisters not to have reached their full potential by the time they gain the shawl. The Aes Sedai have an innate fear of the seduction of saidar, they don't encourage any heavy channeling early on, working on building strength of will of the women first.
The sul'dam rather train damane intensively and daily. They mean them to gain their full strength as fast as possible.
In fact, once the news of Rand drawing Callandor reached the Tower, the training program should have been ramped up to force EVERYone. They say the more you bleed in training, the less you bleed in battle. Maybe if they'd have been more willing to burn out or kill a handful of otherwise insignificant channelers in the year or so leading up to the Last Battle, more would have survived in the end.
“Tolerance is the virtue of the man without convictions.” GK Chesteron
Inde muagdhe Aes Sedai misain ye!
Deus Vult!
*MySmiley*