This article is an excerpt from our Sefer
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On Rosh Hashanah one is only allowed to blow the Shofar in order to fulfill the Mitzvah, or for practice for that day. It is forbidden to blow it casually, or for practice for the next day. It is however permitted for children to practice blowing the Shofar on Rosh Hashanah even for no need at all. See Chapter 10 Halacha 24 for the full details of this matter!