5 year old preschooler - tantrums and defiant behavior - daily - what to do?

I'm thinking everything BUT ADHD (overused diagnosis). So many times, educators label misbehavior as ADd/ADHD when it is just a kid who just isn't ready for long sit-down academic learning. Since he was once not too bad, I am concerned he may be feeling stressed from a long day. Stress in a child can cause the lil one to turn in, or act outward. Is he in a program all day? He may be ready to 'call it a day' and just be at home with mom. He may need some quiet 'down time'. Another issue, some boys just are not developmentally ready at this age for a long academic program. Is he able to wiggle and move? Is there a balance of free choice/teacher choice activities, quiet and noisy? Or, can he be feeling 'lost in the pack'. Also, try picture cue cards. Just draw a simple line drawing pix of an activity, such as a ball / car / trike / paint / book. You can give him an option to pick one when it is art/gym/play time. Also, you can have pix cues to let the boy know it will soon be clean-up time. I use a pix of the daily schedule, and I can point to the pix to let a child know it will soon be time for another activity. I heard about pix cues, and I thought that was a crazy idea. It has always worked on the kids that throw tantrums. One boy, he screamed every time we walked into the gym, and then when we left. I had him pick between two things to play with in the gym (car / ball). He picked the car pix. I could tell he was very anxious, and stressed about his choice. When he got there, he turned his card in for the car. As he gained confidence, we picked between three things, then one day he said "I don't need those cards anymore." I think sometimes we tend to 'talk a kid to death' with positive discipline. Be clear. Offer two or three choices. Set limits.