Corrected age and swimming lessons

My boys were born 9 weeks premature, which means that their corrected age is
about 2 months less than their absolute age.

I'm looking at enrolling us in a waterbabies program that Parks&Rec runs:
where babies are introduced to the swimming pool. Babies have to be 6mos at
the time the course starts, which means the boys will be of age either in
November or in January, depending on which age I use.

I want to enroll as soon as possible, but I want to know the boys will be
ready and safe. What things do you think, developmentally, would be
necessary prerequisites for the boys to be introduced to the water? How
strictly should I adhere to corrected age and when should I use the absolute
age(for example: their neck and head control was *much* better than a 1mos'
when they were 1 mo corrected).

TIA for the advice.

Marie
Chris & Alex--born 04/23/03 at 31 wks gestational