Good heavens! Medication is only appropriate if your son has been evaluated and diagnosed by a medical professional with ADHD. Are you ignoring an evaluation that has made you angry, or are you just assuming that those parents with kids who do take medication would give it to them at the first sign of trouble? You are not doing your son any favors by takeing a hard line attitude with a poor understanding of one fo the causes of what you are seeing and a black and white dismissal of a (far off) but potential cause.
That said, kids don't generally become "lazy" without some cause. Since I work as an educational advocate, I see many kids who are branded as "lazy" and I have to say, for 99.99% of them who are evaluated, there is a cause, and it is not always ADHD, and many need no medications.
4th grade is a time that many kids become overwhelmed by visual demands. The first thing I suggest to parents whose kids have a sudden problem is that they find a developmental optiomitrist (call the nearest children's hospital's occupational therapy department for a referal.) This kind of optomitrist can check for accuity (how well he sees) and how well he uses his eye muscles and how efficently he processes visual information. This will cost you no more than a regular eye exam, which he needs anyway. You may feel really badly if he is not just lazy.
Read "The Myth of Laziness" by Dr. Mel Lavine. he has many explainations for why kids suddenly seem lazy. If you could help him, wouldn't you want to?