Just to introduce myself, I am one of the science divers (A4, 200+ hours) at the lake. First, you need to take the "diving for science" class they offer. It takes a weekend and I THINK that you will pay the normal rate of $230 per instructor/divemaster in the water. I seem to recall that the Aquarena center raised the instructor rate recently. I would assume that you should provide documentation regarding your certification and insurance.
Once that is all done, you need to contact the dive coordinator to set a date and the number of students. Aquarena's permit/regulations have a limit on the number of divers allowed in the training area at any one time (the last number I heard was 10), so you may not get your "perfect schedule" every time (especially in the winter). Be sure to bring your "authorization email", don't assume that they know you are coming. That should cover the stuff you need to get in advance of your class.
Once you get there, Check in with the PIC, exchange money, sign the dive logs, coordinate with the staff to get the time for your boat tour of the lake (a pain, but mandatory 45 minutes). Tell your students that you will be gearing up at the south end of the park on the concrete pad next to the "Landing". Bathrooms, picnic tables and changing areas are there. The tables adjacent to the training area are reserved for science divers now unless you have a really quick turn around for your dives. This is a relatively new arrangement and your students will have to walk about 100m each way. Bring all the tanks you will need for the weekend. They do have a compressor on site, but may not have someone to fill tanks for you.
If I were running the class, the first day would be a Aquarena and the second day at Lake Travis. The training area at Spring Lake is just deep enough for certification, but your students would be better served if they could go deeper than the minimum before you them pass.
Another option is the Comal River. Just south of San Marcos, but I don't know that pond.
Hope this helps! PM me for addresses you will need to get "the" answer.