This question concerns the Ashkenazic practice.
I was always told that the tallit katan (worn under clothing, every day, starting in preschool years) got the bracha of al mitzvat tzitzit, but the tallit gadol (worn over clothing during prayers, starting when one is married) gets lehit'atef batzitzit. (The Ramah in Shulchan Aruch says we're not sure the minor garment warrants the proper blessing of lehit'atef.)
I was also told that once you get married, you stop saying a bracha on the talit katan and just rely on the bracha you'll say that day on the talit gadol.
Is that the standard practice? And where is the source please? (I looked at a shulchan aruch and saw it talked about that occasionally you can wait for the later bracha to include it, but did it say that you should?)