My 10 year old daughter tried Strattera after being on Adderall XR for about 2 years. Initially, I was very hopeful as she seemed so much more aware of her environment but that didn't last but for about one month. It never really helped her focus or attention. After about 3 months we gave up as the side effects weren't worth the little help it was giving her. Strattera made her extremely hot and sweaty, possibly even elevated blood pressure, and she had really bad headaches. Towards the end of her trial, she was starting to get moody and irritable. Her doctor told me that she was very disappointed in Strattera as it hadn't had the success the medical community was hoping for.
On the positive side, I know of 3 children first hand who've had success with it. One parent even goes as far as to call it a miracle drug for her daughter. Like everything else, it boils down to the individual. Strattera is like other anti-depressants, it takes several weeks to months to see it's full effects. I know you called it an SSRI but I don't believe it's classified as such because instead of working on seratonin, it works on a neurotransmitter that starts with an "N" and I can never remember it's name. I know many people who have switched from Adderall to Strattera did so gradually. Wean the Adderall as you give Straterra time to work.
Hope this gives you some insight.