Most people are only defensive when they feel that they are being attacked. Your attitude toward the teacher will make a big difference in how successful you are in resolving this situation in a pleasant way. Focus on building a partnership with the teacher to help your child and avoid criticizing her methods, especially playing games in class.
Ask the teacher why your son is getting bad grades and what can be done to improve them. Determine what subjects are causing him the most trouble and whether he is working on grade level. You will also want to address the issue of why it takes your son so much longer than the other students to finish his work. Find out what help is needed to get him back on track.
At the meeting, you should talk about your son not being able to concentrate on finishing his work when the other children are "playing." Work with the teacher to find ways that your son can complete his work in a quiet place.
Many people feel that children are just "playing" when actually they are doing educational activities. Remember, teachers want children to enjoy learning so games are often an integral part of their lesson plans. Games are a good way for children to learn new concepts and review old ones.
Hopefully, your son will be able to join in the fun with his classmates soon.