I think it all depends on whether the brain chemistry is the "right" one for ritalin. My boy, though certainly hyperactive and ASD, reacted really badly to concerta (same family as ritalin). It made him calm for 2 hours, that part went really well at school, but then for the rest of the day he was manic, violent (unusual for him) and became really routine-bound - became fixated on me and DD sitting absolutely still in the same chairs, same positions, for hours. Tantrum from hell if we so much as crossed our legs. It was really odd, like his brain had become all jangled up. He also lost loads of weight and in the end I think it contributed to his leaving mainstream as his moods and aggression became really bad. He was just not the happy, easygoing, smiley boy of old. It was, in the end, too much of a price to pay for that blissful 2 hour period of calm, where he could work and concentrate.
My theory, looking back is that it only works for kids with a certain kind of ADHD/hyperactivity, whereas perhaps my boy's is just part of his autism, rather than a separate hyperactivity diagnosis if you see what I mean. He actually doesn't now qualify for an ADHD diagnosis, as is now able to work calmly at school (mainly due to the ABA).
Or, maybe I should have gone for the slow release, and then there would have been less of a chemical "dump" as the drug wore off.
We also tried strattera, and we tried a combo of the two, so we gave it a good shot. But I still wonder about it all.
Am v glad it is going well for you, sorry for tale of woe, but will be v interested in your progress. There is a boy at DS's school whose mother cannot sing the praises enough of ritalin, says it has transformed her boy's and her family's life 10000% for the better. So don't listen to me!