There is no single answer. Some countries allow visa-free travel or have specific agreements for school groups, while others require visas for all nationalities. The requirements will also vary depending on the length of stay.
To determine if a visa is needed, you must check the visa requirements of the destination country for the specific nationalities involved. The best resource is the embassy or consulate of the destination country in the country of origin. You should contact them well in advance of the trip.