Hi M.,
You might want to try moving his bedtime even earlier to 7:00. If your son is overtired at nap time, his adrenaline will kick in and make it nearly impossible for him to fall asleep at nap time. You might also want to try putting him down for his nap earlier -- 12:30, 12:00. Moving his nap later will only make the problem worse. He could be growing out of his nap, but having watched not just my son but also dozens of kids of his preschool (starts at age two) go through this, many kids stop napping gradually, but all the two year-olds at his school (about 30 kids) napped until they were closer to three, at which point some started dropping naps a few days a week while others would not sleep during the week but would take 3 hour plus naps on weekend days. Our son stopped napping at 11 months (the same age I stopped napping -- permanently). I could have decided that 11 months is just when both of us were ready to stop napping, but I just couldn't believe that. Both my instincts and everything I had read said otherwise. I found a sleep expert through my pediatrician's office (my friend had also recommended the same person). It turns out we were over soothing our son at nap time. The expert told us to simply turn off the light, pull his shades, read one book to him (not in his bed) while he held his favorite stuffy, put him in his crib/bed, tell him to have a good rest (never say the words sleep or nap), tell him that I would be in the house the whole time he rested, and leave. She also stressed the importance of noticing the very first signs that he was tired and start that brief process immediately, before his adrenaline kicked in. Often, we didn't wait for any signs because it was nap time, and the adrenaline can kick in so quickly. This literally worked the first day we tried it. Another thing that helped when our son was closer to your son's age, is that we told him that his favorite stuffed animal, Monkey (ok, not the most creative namer!), needed to rest. We asked our son to keep quiet for Monkey, and inevitably our son would fall asleep. Finally, you might want to check out the book "Healthy Sleep Habits, Happy Baby." It is written by a doctor who ran (runs?) the sleep clinic at the U of Chicago Med Center. While the author, Weissbluth, can be a bit extreme on the cry it out stuff, his book contains a ton of information about how much sleep kids need at different ages, what happens to brain development during naps, the percentage of kids at various ages with certain bedtimes and hours of sleep, and strategies for various sleep problems in the context of actual cases. Again, you might need to ignore one or two things where, for us, he went a bit too far, but we found almost everything else in the book informative and helpful. Also, you might want to check with your pediatrician's office about finding a sleep expert. Ours didn't even charge us because, from our brief phone consult, she could easily tell what we were doing wrong (singing and rocking and not sending the appropriate signals, e.g., darkening the room a bit first, that it was time to rest before we read to him). Then poof! Gone were the half-hour walks around the neighborhood trying to get him to fall asleep, etc. Trust your intuition (and the numbers). Your son likely does need his nap still. Do not try to move his nap later so that he will be more tired. That strategy will have the opposite effect because his adrenaline will spike (Weissbluth's book explains this well). As the doc says, "Sleep begets sleep." The more rested your child is, the more easily he will sleep. This might sound counterintuitive but because of how adrenaline works, an overtired child has a much harder time sleeping. You were smart to move his bedtime earlier!
Good luck, and I hope some of this helps!
K.