We tried Elmer in Plano once. There was like three classes in the pool at the same time. It was too much noise for my sensory sensitive guy. Maybe if they know it's a special student they design the class differently. Be sure to ask about this if noise is an issue. We never went back.
We had more success going to the wade pool area at Plano Rec. pools. Once he has warmed up on the fun slides, etc. then we go over to the big pool and "swim" around. He's in a life jacket and we are holding him while he practices the movements for swimming. That was last year when he was two. We totally let him go at his own pace which can be slow and fustrating for us but he needs the time and reassurance. Seeing the other kids having fun at the community pool really helped too.