My son will be 9 months old in 6 days.?

He sleeps about 9 hours at night with 2 two hour naps during the day. However, when I put him down at night he wakes up after 1 hour and I have to go in and rock him back to sleep. If I don't he just screams and screams and screams. If he stays at my mom's house he doesn't wake after an hour but sleeps through the night. Any advice on how to get rid of this nightly waking. He goes to bed about 8:30 and sleeps till about 5:30.