There were at least two incidents, Radio B92 in Belgrade, Serbia, reported. Buses were damaged and a number of people injured, including three children, witnesses said.
The buses were carrying worshippers from a celebration of St. Vitus Day at a shrine near Pristina, the Kosovar capital. St. Vitus, a Sicilian martyred under the Roman Empire, is venerated in Slavic countries.
Sava Janjic, a Serbian Orthodox abbott, posted an account of what he said was the most serious attack on Twitter.
"Albanians are en masse stoning Serb school buses. Five buses have been damaged, there are injuries. Witnesses said that groups of Albanianas waited for Serb buses in ambush, some even followed the buses in their cars," Janjic said. "What were Kosovo police doing?"
Kosovo declared independence in 2008 and is recognized by more than 100 countries, including the United States. Serbia, however, has withheld recognition of its former territory.
The country is overwhelmingly ethnic Albanian. Tensions between the Albanian and Serbian communities in Kosovo remain high.