Classes are a good way to socialize your dog, to learn how to work with distractions, and to develop your relationship with each other. However it's vitally important that you observe an instructor and their training methods BEFORE you enroll your dog in classes. If you're not comfortable with an instructor's methods then avoid them. Personally, I encourage you to seek an instructor that promotes 'positive, reward based methods' and strongly recommend that you stay away from traditional training (like Cesar Millan). From my perspective there's a vast difference between those two approaches. The 'positive' approach is all about respectful communication and willing cooperation whereas the 'traditional' approach is based on control and force.
Some books that I highly recommend to anyone with a dog....
Canine Body Language: A Photographic Guide Interpreting The Native Language Of The Domestic Dog (author: Brenda Aloff)
On Talking Terms With Dogs: Calming Signals (au: Turid Rugaas)
Get Connected With Your Dog: Emphasizing The Relationship While Training Your Dog (au: Brenda Aloff)
Aggression In Dogs: Practical Management, Prevention and Behaviour Modification (au: Brenda Aloff)
The Power Of Positive Training (au: Pat Miller)
Control Unleashed: Creating A Focused And Confident Dog (au: Leslie McDevitt)
The Culture Clash: A Revolutionary New Way Of Understanding The Relationship Between Humans And Domestic Dogs (au: Jean Donaldson)
Regards,
Sandy Boyd