the Children's Health Council in Palo Alto ###-###-####) are set up to provide full interdisciplinary evaluations and plans (also treatment if needed). The advantage here is that you may have several professionals looking at different aspects of a potential problem so are less likely to have preconceived notions coloring results or interpretations.
They are quite expensive though they will work with you and your financial situation to try to make it affordable and actually provide a lot of subsidy to various families.
Another advantage is that they work directly on providing an IEP (Individual Education Plan) for school and, I bleieve, will work with the school if needed.
Whoever you see the important thing is to make sure they are a good fit not only for your kids but for you and your husband as well. No matter how clinically great someone is if their communication style is not effective for you or in some other way they seem at odds with you then they are probably not the best choice. Both parents and kids need to feel safe and comfortable discussing anything and asking anything.
You may also want to remind your 17 year old that he has been coping well to date. Even if he is diagnosed with ADD or similar it is no excuse for not living in the real world. He needs to learn to cope with his challenges just like everyone else (we all have challenges of some sort). On the other hand you can also reinforce that if you are concerned there is a problem seeking help and learning your resources is always appropriate so if he is concerned he is doing the right thing to bring it to you and ask for help in finding those resources for evaluation etc.
Good luck. I hope you all find someone you are happy to work with and have great outcomes.
K.